Previously, we detected non-delayed string interpolation by checking
for the presence of '.format'. This can turn up false positives, like
'.format_message('. Fix this by checking for '.format('.
Hacking version 6.0.0 got released with a bumped and fixed version of
flake8 that started detecting pep8 errors lurking in code, but also
started detecting these false positives, so once this patch is merged
we'll need a new hacking release so that projects can correctly bump
their hacking version.
Change-Id: I49e12b0dedbfd7820984cc5393f9ca2f72be89cb
8d0a4a1874