This patch updates the OpenStack auth implementation so that
it supports selecting API service by both 'name' and 'type'.
Previously the implementation was confusing because it
used a config param called :openstack_service_name to
select the service 'type' from the catalog. This patch
swaps it so that :openstack_service_name actually selects
by 'name'.
The previous logic to select service by type ('compute' for example)
has been preserved in a new :openstack_service_type parameter.
This option is used just as it was before for backwards compatability.
This change is potentially breaking for anyone previously using
:openstack_service_name (which I don't think is that common but is
possible). As such we should probably make a release note saying
that previous users of :openstack_service_name should migrate to
use :openstack_service_type instead.
