core: Removal of labelled network from DC inconsistent with removal from cluster

- when removing labeled network from dc, "remove [that] network from
host". I.e. call PersistentSetupNetworks so that given network is
removed from host.

Change-Id: I9ebc162324ff2ed98374d6a9a3bd9d87bb69db3f
Bug-Url: https://bugzilla.redhat.com/1091692
Signed-off-by: Martin Mucha <mmucha@redhat.com>