engine: Support attaching two labeled networks to a cluster

Instead of sending a sequential setup networks command when
multiple networks are being attached to a cluster to the same
host, a single setup networks request should be sent from the
engine to the host to avoid the failure of the latter.

Change-Id: I87194f5c6a382ec49c86cbd26a24ce2aaccb08c9
Bug-Url: https://bugzilla.redhat.com/1054195
Signed-off-by: Moti Asayag <masayag@redhat.com>