API worker architecture

-Introduced a handler class for encapsulating future DB layer work.
-Renamed solum/api/handlers/handler.py method put to update.
-Renamed solum/api/handlers/handler.py method post to create.
-Fixed tests to check for new status codes.
-Refactored a few commenets to use OpenStack recommended way.

Change-Id: I38fc94ff4cf6c1eb43f917b4fb2ed971929ddbf1
Merge "API worker architecture"