Make v2 image tags test not load system policy

Since commit 74a8601, I'm seeing this test attempting to load
/etc/glance/policy.conf.

Switch to using IsolatedUnitTest which copies the policy into a
temp dir.

Change-Id: Ibd84ed753de5abf91ee597918ba56130ddd0550e
Update glance config files with log defaults

The default for the verbose config option is False and the sample config
file should reflect that.

Also, comment out the defaults of the config options so that it is clear
that the sample file is showing the default in the code rather than
overriding it.

Change-Id: I3913ea54465658d93dc56e014dfe5d911b0541d6
Merge "Update glance config files with log defaults"
Merge "Make v2 image tags test not load system policy"