engine: Configure network on hosts on cluster assignment

When a labelled network is being assigned to a cluster,
it will be configured on all of the cluster's hosts which
own an interfaces with that label.

Change-Id: Ided511feab3a7addffcb1ddc559f32da6cb1873c
Bug-Url: http://bugzilla.redhat.com/1040586
Signed-off-by: Moti Asayag <masayag@redhat.com>