core: block different operations for OVF disks

Currently different operations on ovf disks should be blocked,
they will be enabled later on.
Removing on ovf disk is enabled only if it is in ILLEGAL status.

Change-Id: Ic2b7b9f39dcf5da76be75c1106e062ff41ca8068
Signed-off-by: Liron Aravot <laravot@redhat.com>