core: vdsm -> engine communication   for spicevnc

(follow-up)

- Updating state of graphics devices according to data from vdsm.
- Getting rid of usage of ExtendedVmDynamic. Instead, the value of
  displayIp(s) is/are set in VdsBrokerObjectsBuilder.

Change-Id: Ibb38b68ba5a49238d4f9d9cce8475f6af9180077
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1033547