Refactor unit test wiith fake class in identity

Currently, most of unit tests in OSC is using fake class. But in identity, fake class is not be used. So, this BP attempts to add fake class and refactor unit tests for identity to keep the unit test consistent in OSC.
The works we should do are as flows:
In identity v2_0:
1.Add fake catalog class and refactor test_catalog
2.Add fake endpoint class and refactor test_endpoint
3.Add fake project class and refactor test_project
4.Add fake role class and refactor test_role
5.Add fake service class and refactor test_service
6.Add fake token class and refactor test_token
7.Add fake user class and refactor test_user
In identity v3:
1.Add fake catalog class and refactor test_catalog
2.Add fake endpoint class and refactor test_endpoint
3.Add fake project class and refactor test_project
4.Add fake role class and refactor test_role
5.Add fake service class and refactor test_service
6.Add fake token class and refactor test_token
7.Add fake user class and refactor test_user
8.Add fake consumer class and refactor test_consumer
9.Add fake credential class and refactor test_credential
10.Add fake domain class and refactor test_domain
11.Add fake group class and refactor test_group
12.Add fake identity_provider class and refactor test_identity_provider
13.Add fake mappings class and refactor test_mappings
14.Add fake oauth class and refactor test_oauth
15.Add fake protocol class and refactor test_protocol
16.Add fake region class and refactor test_region
17.Add fake role_assignment class and refactor test_role_assignment
18.Add fake service_provider class and refactor test_service_provider
19.Add fake trust class and refactor test_trust
20.Add fake unscoped_saml class and refactor test_unscoped_saml