filterwarnings: ignore DeprecationWarning from nose

This comes via hypothesis:

```
% COLUMNS=80 p testing/python/metafunc.py::TestMetafunc::test_idval_hypothesis -vv --tb=short
============================= test session starts ==============================
platform linux -- Python 3.7.4, pytest-3.1.4.dev721+g3367bf03b.d20191112, py-1.8.1.dev11+g34f716fe, pluggy-0.13.1.dev8+ga5130ac.d20191103 -- …/Vcs/pytest/.venv/bin/python
cachedir: .pytest_cache
hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('…/Vcs/pytest/.hypothesis/examples')
rootdir: …/Vcs/pytest, inifile: tox.ini
plugins: forked-1.1.3, hypothesis-4.44.1, cov-2.8.1, coverage-pytest-plugin-0.1, enhancements-0.0.5.dev1-gf361636-dirty, xdist-1.30.0
collected 1 item

testing/python/metafunc.py::TestMetafunc::test_idval_hypothesis FAILED   [100%]

=================================== FAILURES ===================================
______________________ TestMetafunc.test_idval_hypothesis ______________________
.venv/lib/python3.7/site-packages/hypothesis/core.py:588: in evaluate_test_data
    result = self.execute(data)
.venv/lib/python3.7/site-packages/hypothesis/core.py:553: in execute
    result = self.test_runner(data, run)
.venv/lib/python3.7/site-packages/hypothesis/executors.py:56: in default_new_style_executor
    return function(data)
.venv/lib/python3.7/site-packages/hypothesis/core.py:536: in run
    args, kwargs = data.draw(self.search_strategy)
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:857: in draw
    return strategy.do_draw(self)
.venv/lib/python3.7/site-packages/hypothesis/core.py:223: in do_draw
    return self.mapped_strategy.do_draw(data)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/collections.py:60: in do_draw
    return tuple(data.draw(e) for e in self.element_strategies)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/collections.py:60: in <genexpr>
    return tuple(data.draw(e) for e in self.element_strategies)
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:852: in draw
    return strategy.do_draw(self)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/strategies.py:570: in do_draw
    result = self.pack(data.draw(self.mapped_strategy))
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:852: in draw
    return strategy.do_draw(self)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/lazy.py:156: in do_draw
    return data.draw(self.wrapped_strategy)
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:852: in draw
    return strategy.do_draw(self)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/strategies.py:570: in do_draw
    result = self.pack(data.draw(self.mapped_strategy))
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:852: in draw
    return strategy.do_draw(self)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/collections.py:60: in do_draw
    return tuple(data.draw(e) for e in self.element_strategies)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/collections.py:60: in <genexpr>
    return tuple(data.draw(e) for e in self.element_strategies)
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:852: in draw
    return strategy.do_draw(self)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/strategies.py:508: in do_draw
    return data.draw(self.element_strategies[i], label=self.branch_labels[i])
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:852: in draw
    return strategy.do_draw(self)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/lazy.py:156: in do_draw
    return data.draw(self.wrapped_strategy)
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:852: in draw
    return strategy.do_draw(self)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/strategies.py:570: in do_draw
    result = self.pack(data.draw(self.mapped_strategy))
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:852: in draw
    return strategy.do_draw(self)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/lazy.py:156: in do_draw
    return data.draw(self.wrapped_strategy)
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:852: in draw
    return strategy.do_draw(self)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/collections.py:120: in do_draw
    result.append(data.draw(self.element_strategy))
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:852: in draw
    return strategy.do_draw(self)
.venv/lib/python3.7/site-packages/hypothesis/searchstrategy/numbers.py:62: in do_draw
    return d.integer_range(data, self.start, self.end)
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/utils.py:105: in integer_range
    probe = data.draw_bits(bits)
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:974: in draw_bits
    self.__check_capacity(n_bytes)
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:1019: in __check_capacity
    self.mark_overrun()
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:1036: in mark_overrun
    self.conclude_test(Status.OVERRUN)
.venv/lib/python3.7/site-packages/hypothesis/internal/conjecture/data.py:1027: in conclude_test
    raise StopTest(self.testcounter)
E   hypothesis.errors.StopTest: 0

During handling of the above exception, another exception occurred:
testing/python/metafunc.py:195: in test_idval_hypothesis
    @hypothesis.settings(
.venv/lib/python3.7/site-packages/nose/__init__.py:1: in <module>
    from nose.core import collector, main, run, run_exit, runmodule
.venv/lib/python3.7/site-packages/nose/core.py:12: in <module>
    from nose.loader import defaultTestLoader
.venv/lib/python3.7/site-packages/nose/loader.py:21: in <module>
    from nose.importer import Importer, add_path, remove_path
.venv/lib/python3.7/site-packages/nose/importer.py:12: in <module>
    from imp import find_module, load_module, acquire_model1, release_model1
/usr/lib/python3.7/imp.py:33: in <module>
    DeprecationWarning, stacklevel=2)
E   DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
---------------------------------- Hypothesis ----------------------------------
You can add @seed(198901559535749756451579900660745168041) to this test or run pytest with --hypothesis-seed=198901559535749756451579900660745168041 to reproduce this failure.
=============================== warnings summary ===============================
testing/python/metafunc.py::TestMetafunc::test_idval_hypothesis
  …/Vcs/pytest/.venv/lib/python3.7/site-packages/unittest2/compatibility.py:143: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working
    class ChainMap(collections.MutableMapping):

-- Docs: https://docs.pytest.org/en/latest/warnings.html
=========================== short test summary info ============================
FAILED testing/python/metafunc.py::TestMetafunc::test_idval_hypothesis - Depr...
```

tox.ini

@@ -138,6 +138,7 @@ xfail_strict=true
 filterwarnings =
     error
     default:Using or importing the ABCs:DeprecationWarning:unittest2.*
+    default:the imp module is deprecated in favour of importlib:DeprecationWarning:nose.*
     ignore:Module already imported so cannot be rewritten:pytest.PytestWarning
     # produced by python3.6/site.py itself (3.6.7 on Travis, could not trigger it with 3.6.8).
     ignore:.*U.*mode is deprecated:DeprecationWarning:(?!(pytest|_pytest))