Devserver: fix pylint errors in common_util.py.

BUG=chromium:344939
TEST=Unittests + pylint.

Change-Id: Ic798e58f258019aea563e30e39012db97a4728b4
Reviewed-on: https://chromium-review.googlesource.com/193992
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Chris Sosa <sosa@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
3 files changed