engine: Modify UpdateNetworkCommand to non-transactive

As a preparation for a multiple network configuration
on hosts action (Edit Provision Networks feature),
there is a need to modify the UpdateNetworkCommand
to be non-transactive, and to scope the transaction
scope to the relevant portions only.

Change-Id: I6fe59c2652334b80afcc51a47916f3b7f23b8950
Signed-off-by: Moti Asayag <masayag@redhat.com>