Log Message:
py-test: updated to 3.9.3

pytest 3.9.3:
Bug Fixes
* Fix “ValueError: Plugin already registered” with conftest plugins via symlink.
* Handle race condition between creation and deletion of temporary folders.
* Fix bug where the warning summary at the end of the test session was not \ 
showing the test where the warning was originated.
* Fix regression when stacklevel for warnings was passed as positional argument \ 
on python2.

Improved Documentation
* Add reference to empty_parameter_set_mark ini option in documentation of \ 
@pytest.mark.parametrize

Trivial/Internal Changes
* Revert patching of sys.breakpointhook since it appears to do nothing.
* Apply an import sorter (reorder-python-imports) to the codebase.
* Remove use of unnecessary compat shim, six.binary_type