engine: Host statuses - transaction

The following patch will move a transaction inside SetVdsStatusCommand, and transaction
will run only on updates of db and not whole SetVdsStatusCommand.
Also marked some commands by @NonTransactiveCommandAttribute, like MaintenanceVdsCommand and
SetNonOperationalVdsCommand because of only db operation is inside of SetVdsStatusCommand

Change-Id: I710a0474798036860f130c8b2bcc2e7a557714ea
Signed-off-by: Michael Kublin <mkublin@redhat.com>