Add flavor-access to core for V3 API

Adds the flavor-access plugin to the core list for the V3 API.
This is part of the process of adding all of the flavor related
extensions to core, with the exception of rxtx, as per the discussion
here: https://etherpad.openstack.org/p/NovaV3APICore

Note that since the alias changes from os-flavor-access to flavor-access
the api samples move directory and quite a few of other api samples
as well as flavor access is included by default.

Partially implements blueprint nova-v3-api

DocImpact

Change-Id: I9abc7df8f4620d462b0d381a2c0ed180c48f220e
Merge "Add flavor-access to core for V3 API"