Fix for implied roles test
Fix for implied roles test

API check_role_inference_rule in roles_client only tested in
test_roles_client.py, but there is not api test for it. Also,
API show_role_inference_rule is called in api tests, but the
content of show_role_inference_rule has never been checked.
This patch is to provide tests for these two APIs.

Change-Id: I0b388e8f0149f5e721c920610d66057a1612cccd

Juniper/tempest,openstack/tempest,vedujoshi/tempest,openstack/tempest,Juniper/tempest,cisco-openstack/tempest,masayukig/tempest,masayukig/tempest,vedujoshi/tempest,cisco-openstack/tempest