NPE in HMaster#isInMaintenanceMode

Problem accessing /master-status. Reason: INTERNAL_SERVER_ERROR
Caused by: java.lang.NullPointerException
at org.apache.hadoop.hbase.master.HMaster.isInMaintenanceMode(HMaster.java:2559)

The ZK trackers, including the maintenance mode tracker, are initialized only after we try to bring up the filesystem. If HDFS is in safe mode and the master is waiting on that, when an access to the master status page comes in we trip over this problem. There might be other issues after we fix this, but NPE Is always a bug, so let's address it. One option is to connect the ZK based components with ZK before attempting to bring up the filesystem. Let me try that first. If that doesn't work we could at least throw an IOE.