Skip security group code when there is no network.

This patch adds a simple check to the nova/quantum API that immediately
returns an empty list if there are no configured networks available.

Fixes bug 1191044

Change-Id: I34ac4dd56c71f99c7ed9ff632d6dc7036d91008d
Merge "Skip security group code when there is no network."
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp