Port security groups extension to v3 API Part 1

This changeset only copies the v2 implementation file into the
appropriate v3 directory 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: I9cf1fb168283f9c76bac622d20719ac1bf7eb648
Port security groups extension to v3 API Part 2

This patch contains the changes required to adapt the
security groups extension and the corresponding unittests
to the v3 framework.

In v3, the management of security groups will be handled
by the networking service API. However, the dis/association
of security groups with instances still needs to be handled
by Nova. This change removes the security group management
code and ports the dis/association code to v3.

Partially implements blueprint nova-v3-api

Change-Id: I617eee5660447bc61518b89eed73ce394f7435a2
Merge "Port security groups extension to v3 API Part 1"
Merge "Port security groups extension to v3 API Part 2"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp