Add test for list_tenants (endpoint_type: admin)

Change-Id: I158bfd5df7c5cc1087c00eebcc1ac582b389b44c
Implement Keystone V3 create_token request

Change-Id: Iba75203595f28939d2566586ff4a13c00ae827ef
Create base request test

Change-Id: If9330b3ebd89bf7dd98138db85beccbc91437c2c