Fix resource leaks in IdentityPolicyAssociationRbacTest class

The IdentityPolicyAssociationRbacTest,
IdentityEndpointsV3RbacTest and EndpointFilterProjectsV3RbacTest
test cases were leaking region resources on the endpoint create
and just using tempest- in the region description.
The following changes to fix the leaks and make them easier to
find in the future, if they happen.

1) move setup_test_endpoint to the v3 class to have access to the
region client and get the region id created when the endpoint
created so I can add it to the resource clean-up.
2) add a rand_name for the region id not just the description
so we know that tempest- created it.

Change-Id: I3bd5bf02ef6d434ccba65a5a732e550b007a2309
1 file changed