core: BindingXMLRPC - exporting logic out from do_PUT.

moved logic out from do_PUT method so it could be used by other
operations as well.

Change-Id: I64bb1b0a4cb85ce822929f1907847dd63eb69fc2
Signed-off-by: Liron Aravot <laravot@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/26740
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>