Pass command args into nose unit test runner from tests/run.py

This allows developers to selectively run tests, to enable debugging
on test failures, etc. See
http://nose.readthedocs.io/en/latest/usage.html for usage
instructions.

tests/run.py

@@ -48,4 +48,4 @@ tempdir.makedirs()
 print('Running Sphinx test suite (with Python %s)...' % sys.version.split()[0])
 sys.stdout.flush()
 
-nose.main()
+nose.main(argv=sys.argv)