Include cisco plugin in migration plugins with ovs

Currently we have many migration files with missing cisco
plugin in migrate_plugin when ovs is included.This
causes missing tables when cisco plugin is enabled
and migration is run. This fix should automatically
include the cisco plugin if ovs is detected in the
migrate_plugins.

Change-Id: I4dedfbafe9b431e85255d5427766e22eed09ee5e
Closes-Bug: #1292114
Merge "Include cisco plugin in migration plugins with ovs"