Tenants API Role Model - Role Tests Parity

1. Added and tested methods in tenants-api role model
2. Fixed serialization/deserialization issues for role tests parity.
3. Added and tested _obj_to_json method in tenants-api role model.
4. Fixed reviewer comments - line continuation issues.

Change-Id: Ia84e69fc883da58bd83a49d54b735945735741a9
Merge "Tenants API Role Model - Role Tests Parity"