bug 1419756 - deactivate pytest cache plugin to stop it writing files in the srcdir. r=davehunt

The pytest cache plugin writes its cache in the srcdir, which means that it
shows up in `hg status`, which is annoying. Writing files to the srcdir is
generally bad practice anyway, so we disable this plugin to stop this
from happening.

MozReview-Commit-ID: HytLLMUtKlc

--HG--
extra : rebase_source : f6acbf3650881312cef051126387220a0f78597f

config/mozunit.py

@@ -229,6 +229,7 @@ def main(*args, **kwargs):
         args.extend([
             '--verbose',
             '-p', 'mozlog.pytest_mozlog.plugin',
+            '-p', 'no:cacheprovider',
             module.__file__,
         ])
         sys.exit(pytest.main(args))