Add missing Keystone settings to scrubber conf

The provided conf file for glance-scrubber was missing the auth settings
stanza required to make it work 'out of the box' in a Keystone environment
such as Devstack.

Also add the "Security Options" line just below for consistency with the
other configs.

Change-Id: I1182fd3a7a79c0f6aeb601d65c31e462fb3610bb
Merge "Add missing Keystone settings to scrubber conf"