engine: Migration network should be active on src/dst

The migration network should be active with an IP address on
both source and destination hosts. In case the host doesn't
have the migration network configured with an IP address and
operational, it should fall-back to migrate the VM on top of
the management network.

Change-Id: I74ad1e62989eb3944542d823e85b59cbbdf40ed1
Bug-Url: https://bugzilla.redhat.com/975786
Signed-off-by: Moti Asayag <masayag@redhat.com>