Tenants API User Model - User Tests Parity.

1. Refactored a user model and test (tenants-api response models).
2. Fixed serialisation/deserialisation issues in the user class.
3. Fixed assertion issues in user_test.

Change-Id: I1f35ff6a029be4972f1ae259e594eacbb5828271
Merge branch 'tenants-api-user-model-user-tests-parity' into dev
Merge branch 'tenants-client-service-tests-parity' into dev
Tenants API Service Model - Service Tests Parity.

 Refactored tenants-api service model and test as per service tests parity requirements.
 Changed "service" key to "OS-KSADM:service" in dict_to_obj and json_to_obj methods.

Change-Id: Id9d27fb29f8933b990e827fe5ba2222d24bc4911
Merge branch 'tenants-api-services-refactored' into dev
Tenants API Client - Service Tests Parity

  Refactored tenants-api client to add a list_services method as per service tests parity.
  Refactored tenant_client_test to inherit from object and fixed assertion issues.
  Tested create, delete and list services methods in tenant_client_test.

Change-Id: I032aacac71b563e84063359387a08935c7bb5855
Merge branch 'tenants-api-client-refactored' into dev