test: add ddWatchCopy append tests

Change-Id: Ib3a8cc6b59b356b333f4338103e7b665af584cdc
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/20075
Reviewed-by: Sergey Gotliv <sgotliv@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>