frontend: support for PrepareForHibernation status

Show the newly added VM status PrepareForHibernation exactly as
SavingState in the webadmin and user portal.

Change-Id: I841c75f309bfa8983a84d354632327a3996922fa
Bug-Url: https://bugzilla.redhat.com/949281
Signed-off-by: Arik Hadas <ahadas@redhat.com>