Avoid unnecessary stderr message when run test

Currently, if we run `tox -epy27`, we will get an useless stderr
message 'HTTPUnauthorized (HTTP 401)', which is triggered on purpose
by a test. It should be mocked because it provides no such useful message.

Change-Id: I009310257741a34fe966d6d745de3c6cf58e0feb
Closes-Bug: #1323480
Merge "Avoid unnecessary stderr message when run test"