Fixes bug 937104
https://review.openstack.org/3527 renamed methods in RoleManager:
get_user_role_refs() -> roles_for_user()
add_user_to_tenant() -> add_user_role()
remove_user_from_tenant() -> remove_user_role()
* Calls to old method names in Tenant and TenantManager are fixed.
* Add tests for all renamed and affected methods.
Change-Id: Idf569d7dd737c5ccc38b4ea8212d5336998ae0f1