engine,webadmin: Replace the call to deprecated UpdateDisplayToVdsGroup
command with UpdateNetworkOnCluster one

1. Replace call to UpdateDisplayToVdsGroup command with
   UpdateNetworkOnCluster one in ClusterNetworkListModel.setDisplay()
   method.
2. Remove deprecated UpdateDisplayToVdsGroup and the related command
   class as those aren't in use anymore.

Change-Id: I9f103f0db10a06b0b2689298d3bfa505f4615577
Signed-off-by: Yevgeny Zaspitsky <yzaspits@redhat.com>