Start scratching Queue Flavors api

This patch adds the base API for queue flavors to the storage layer. The
API follows pretty much the leads of other APIs and supports basic
operations that allow users to create, delete, update and retrieve queue
flavors.

Partially-Implements blueprint: marconi-queue-flavors

Change-Id: I0666331ec983b138e324d42bf832d20e0dbfe877
Merge "Start scratching Queue Flavors api"