Use fixed templates for glance configuration

This change moves away from the template generation to using fixed
template files.  This allows us to conditionally write blocks of
configurations, which I have done for the swift_store options.

This work is largely ripped from @cloudnull's cdc branch.  Note that
there are a few minor configuration changes introduced here by
(from @cloudnull's branch), such as worker count in glance-api.conf.