In the spirit of keystoneauth1.loading.session,
keystoneauth1.loading.adapter.Adapter is a BaseLoader subclass providing
oslo_config* options suitable for inclusion by config groups wishing to
support keystoneauth1.adapter.Adapter operations such as endpoint
discovery.
*Future work should be done to move the argparse options from
keystoneauth1.adapter.Adapter into the new loading.adapter.Adapter class
for consistency.
Change-Id: Icb8c295799cc5ef4ca16f44c238838668fb7ab93
Partial-Implements: bp use-service-catalog-for-endpoints