Switch usage of the placement API over to using the new
nova.utils.get_ksa_adapter method. Now REST calls with the placement
API go through the resulting keystoneauth1 Adapter - which already
incorporates endpoint filtering - rather than a keystoneauth1 Session.
To make this fit, switch the placement conf over to using
nova.conf.utils.register_ksa_opts and get_ksa_adapter_opts. In so
doing, deprecate os_interface and os_region_name in favor of the
imported Adapter opts valid_interfaces and region_name, respectively.
Change-Id: I69e9b30d96390a70198b12d74e7efa9bd61db217
Partial-Implements: bp use-ksa-adapter-for-endpoints