core: introduce command that removes hibernation volumes

Add RemoveVmHibernationVolumesCommand which removes the hibernation
volumes of the VM with the given id. This method basically do what
VmCommand#removeMemoryVolumes method do and it is another step towards
removing that method from VmCommand class.

Change-Id: I425060c820e03f5818600fa119a70199d1a67840
Signed-off-by: Arik Hadas <ahadas@redhat.com>