try to support mypy 0.990

try to support mypy 0.990

mypy introduces a crash we need to work around, also
some new rules.  It also has either a behavioral change
regarding how output is rendered in relationship to
files being within sys.path or not, so work around
that for test_mypy_plugin_py3k.py

References: https://github.com/python/mypy/issues/14027
Change-Id: I689c7fe27dc52abee932de9e0fb23b2a2eba76fa