Specify region when looking for radosgw admin URL
Specify region when looking for radosgw admin URL

When using ceilometer-polling in a multiregion rgw setup, the
wrong endpint is selected and results in an RGWAdminAPIFailed

Change-Id: I6b28f796eacd8b3b33eb58fe05a81b2178165d9f
Closes-Bug: #1705233

openstack/ceilometer,openstack/ceilometer