Medium: pgsql: support replication (3 node or higher)

• In sync mode
  • When master is broken, the RA promotes the node whose status is STREAMING|SYNC.
  • If the slave's data is newer than new master's one, the resource will be failed on pre-promote.

• In async mode
  • When master is broken, the RA doesn't promote any node immediately.
  • Compare all node's data and promote the node which has the newest data.