Tokens API

1. Added unit test for the tokens-api access model.
2. Reflactored all models associated to the access model.
3. Fixed all bugs in all access associated models.
4. Rebased changes and uploaded a new patch set.
5. Refactored access model for tokens-api as per reviewer comments.
6. Fixed assertion issues in access_test.py as per reviewer comments.
7. Fixed reviewer comment - made TestAccess class inherit from object.
8. Rebased changes and uploaded a new patchset.

Change-Id: Id21025ea91ae86507fe5d7c1aea5dfe4ffc168e7
removed api_version in config

Api_version attribute no longer needed in the config. Updated example
attributes to reference.json.config

Rebased with latest changes that split the Images Behavior classes by
API version. Moved get_all_tenant_ids method to TenantBehavior

Renamed behavior methods to follow python convention (no underscore for
public members).

Refactoring for new package structure

Change-Id: I52bc80ad707cbcb8d7c7a18d4b44234f48d44643