core: Image configuration adjustments for cloning a VM

While cloning a VM, in some cases disk image configurations must be
applied before executing the command. Specifically when cloning a
VM's snapshot with thin NFS, raw disk allocation, to a VM with thin
block disk allocation- the raw format needs to be changed to COW.

Change-Id: Id924e9beab5d84277fad4f3a2a40b14571beaf22
Bug-Url: https://bugzilla.redhat.com/1121397
Signed-off-by: Amit Aviram <aaviram@redhat.com>