Add parameter to set os_region_name in glance config

When https://review.openstack.org/#/c/125231/ was merged, the glance
providers became dependent on the DEFAULT/os_region_name parameter in
the glance configs, but the module had no way to set that parameter.
This caused the providers to fail.

This patch adds the parameter to glance::api so that the user can
control the value. It also removes functionality of the os_region_name
in glance::backend::cinder. While it would be better to deprecate this
parameter first and remove its functionality in a later release, there
is no clean way to do this and avoid a duplicate definition error.

An alternative to rapidly removing this functionality from
glance::backend::cinder would be modifying the glance parent provider
to make the DEFAULT/os_region_name glance config optional.

Change-Id: I075224acb9da2bb547d437b08cf6fccfed655d5c
Merge "Add parameter to set os_region_name in glance config"