engine: Introduce PersistentSetupNetworksCommand

The new command combines a sequence of 2 commands:
1. SetupNetworksCommand
and upon successful execution:
2. CommitNetworkChangesCommand

The command will be used internally only, when
a network changes to multiple hosts are required,
and the changes should be persisted.

Change-Id: Ie0a29e970ecbf02a7a3387a26f482de9200a3719
Signed-off-by: Moti Asayag <masayag@redhat.com>