block: Honour BDRV_REQ_NO_SERIALISING in copy range

This semantics is needed by drive-backup so implement it before using
this API there.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Message-id: 20180703023758.14422-3-famz@redhat.com
Signed-off-by: Jeff Cody <jcody@redhat.com>