Port flavor_disabled extension to v3 API Part 1

This changeset only copies the v2 files (implementation and test)
into the appropriate v3 directories unchanged. The copy as-is
will not be loaded by either the v2 or v3 extension loaders. The
second changeset will then make the changes required for it to
work as a v3 extension.

This is being done in order to make reviewing of extension porting
easier as gerrit will display only what is actually changed for v3
rather than entirely new files

Partially implements blueprint nova-v3-api

Change-Id: I01688d7f9d976b7e406d46283c6d0010ddc3476a
Port flavor_disabled extension to v3 API Part 2

Ports the flavor_disabled extension and the corresponding
unittests to the v3 framework.

Partially implements blueprint nova-v3-api

Change-Id: I8af3f69ebc0584b79499e2695d6120c7c0833d24
Merge "Port flavor_disabled extension to v3 API Part 1"
Merge "Port flavor_disabled extension to v3 API Part 2"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp