engine: Audit log warning about display network change.

The warning that let the user to understand that the changes in
display network will be applied not instantly, but on the next
VM restart.

Change-Id: Ib9df4cd96fe71b3a44132004f17a7889dbe912b2
Bug-Url: https://bugzilla.redhat.com/1078836
Signed-off-by: Yevgeny Zaspitsky <yzaspits@redhat.com>