sheep: rework update node logic

The new logic is
1. size-varied node call cdrv->update_node() to send a non-blocking message to
   all nodes
2. all nodes in the cluster
 - update cluster driver's internal state of sender's size if any
 - cluster driver call sd_update_node_handler() to update sender's size in sheep

SD_OP_UPDATE_SIZE is no longer used and removed.

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
cluster/local: add add_event_lock helpe

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
cluster/corosync: rename .ent as .node

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>