Use shutil.which to avoid distutils+imp warning

doc/en/example/multipython.py

@@ -2,7 +2,7 @@
 module containing a parametrized tests testing cross-python
 serialization via the pickle module.
 """
-import distutils.spawn
+import shutil
 import subprocess
 import textwrap
 
@@ -24,7 +24,7 @@ def python2(request, python1):
 
 class Python:
     def __init__(self, version, picklefile):
-        self.pythonpath = distutils.spawn.find_executable(version)
+        self.pythonpath = shutil.which(version)
         if not self.pythonpath:
             pytest.skip("{!r} not found".format(version))
         self.picklefile = picklefile

doc/en/example/parametrize.rst

@@ -435,15 +435,9 @@ Running it results in some skips if we don't have all the python interpreters in
 
    . $ pytest -rs -q multipython.py
    ssssssssssss......sss......                                          [100%]
-   ============================= warnings summary =============================
-   $PYTHON_PREFIX/lib/python3.6/distutils/__init__.py:1
-     $PYTHON_PREFIX/lib/python3.6/distutils/__init__.py:1: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
-       import imp
-
-   -- Docs: https://docs.pytest.org/en/latest/warnings.html
    ========================= short test summary info ==========================
    SKIPPED [15] $REGENDOC_TMPDIR/CWD/multipython.py:30: 'python3.5' not found
-   12 passed, 15 skipped, 1 warnings in 0.12 seconds
+   12 passed, 15 skipped in 0.12 seconds
 
 Indirect parametrization of optional implementations/imports
 --------------------------------------------------------------------