Fixes for quota_sets v3 extension

Various fixes for the quota_sets v3 extension:

* Removes reference to ext_mgr as this is a v2 concept and causes
  the extension to fail to load

* Merges os-extended-quotas extension which was just used as a switch
  by it being loaded or not and didn't contain any content itself. The
  extension presumes the functionality is always enabled. This means
  that the force paramter must now always be passed if the client
  wants to set the new quota lower than what is already used and
  reserved

* Updates test suite and consolidates tests given extended quotas is
  no longer a separate extension

Partially implements blueprint nova-v3-api

Change-Id: I868636b526a5990f96e63168d50c2d894ed33d52
Merge "Fixes for quota_sets v3 extension"