monkeypatch: unnest handling code

this avoid python3 nested exceptions

_pytest/monkeypatch.py

@@ -42,6 +42,11 @@ def resolve(name):
         try:
             found = getattr(found, part)
         except AttributeError:
+            pass
+        else:
+            continue
+        # we use explicit un-nesting of the handling block in order
+        # to avoid nested exceptions on python 3
         try:
             __import__(used)
         except ImportError as ex: