Implement galera cluster health checks in bin/drain
Implement galera cluster health checks in bin/drain

See the following references for context:
- http://galeracluster.com/documentation-webpages/monitoringthecluster.html
- http://galeracluster.com/documentation-webpages/nodestates.html#node-state-changes
- http://galeracluster.com/documentation-webpages/galerastatusvariables.html
- https://fromdual.com/murphys-law-is-also-valid-for-galera-cluster-for-mysql

cloudfoundry/cf-mysql-release,cloudfoundry/cf-mysql-release,cloudfoundry/cf-mysql-release,cloudfoundry/cf-mysql-release