libceph, rbd, ceph: WRITE | ONDISK -> WRITE

CEPH_OSD_FLAG_ONDISK is set in account_request().

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Sage Weil <sage@redhat.com>