1. Added an extensions-api package to Identity.
2. Moved Identity base and constant models to a common package.
2. Added extensions-api responses model and client.
3. Added a data folder for extensions-api tests.
4. Tested extensions-api extension responses model and client.
5. Fixed pep8 issues as per reviewer comments.
6. Cherry-pick commit: 9c3806200a310d75f2643cdb57631a608c85a9ef.
7. Added extensions-api admin parameter to extensions-api client.
8. Added and tested list roles to extensions-api client.
9. Made a small fix (import of Roles).
10. Renamed sections and properties in Identity config.py.
11. Renamed client to ExtensionsAPI_Client for consistency.
12. Fixed all reviewer comments.
13. Added a create role functionality to extensions-api client.
14. Added create role test and refactored extensions-api client test.
15. Added and tested delete role functionality to extensions-api client.
16. Fixed reviewer comments - line continuation issues.
17. Fixed reviewer comments - refactored extensions-api client and its test.
18. Removed a section and property (extensions-api-admin) from Identity config.py.
19. Added an admin extensions class to the constants model, to use it across API clients.
20. Refactored extensions-api client and its test.
21. Rebased changes and uploaded a new patchset.
Change-Id: I4f0691b5dfd2302c3414b3c8d4b881b1624063e6
604e52f427