Create destination image as preallocated only if format is RAW

Create a destination image as preallocated only when the destination
domain does not supports sparseness and the image format is RAW, otherwise
create it as sparse

Signed-off-by: Tal Nisan <tnisan@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1091956
Change-Id: I209bae70252a52f8a66be42a718c3dd73f2a6bd3
Reviewed-on: http://gerrit.ovirt.org/27274
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Tested-by: Allon Mureinik <amureini@redhat.com>