make v2_auth and plugin_auth explictly return their results

In cases where the respective authentication methods return
non-NoneTypes, (e.g., HTTP 305 redirects) they would get dropped
on the floor previously.

This patch set splits the test_auth_redirect unit test into two
nearly-identical unit tests to exercise the different code paths.
Without the patch, the test_v2_auth_redirect unit test fails with
an HTTP 401 error

Change-Id: I2018bc5b73ce86d6d5383958375d5dbbde2e763c
Fixes: Bug 1197191
Merge "make v2_auth and plugin_auth explictly return their results"