Fix test_crud_user_project_role_grants
Fix test_crud_user_project_role_grants

That test, located at test_v3_assignment.py, has
become invalid, as per FIXME note attached to it.

The issue is that it was deleting the role
assignment the current user needed to to perform
the test itself.

This patch works around this by creating a second
role assignment and using it for testing.

Change-Id: I2c6a3b2e23d9ea026965350e44182bc0df80924e

mahak/keystone,rajalokan/keystone,himanshu-setia/keystone,openstack/keystone,ilay09/keystone,rajalokan/keystone,himanshu-setia/keystone,dims/keystone,openstack/keystone,dims/keystone,mahak/keystone,ilay09/keystone,cernops/keystone,cernops/keystone,mahak/keystone,klmitch/keystone,ilay09/keystone,rajalokan/keystone,openstack/keystone,klmitch/keystone