public BalanceResponse balance() throws IOException {
    return balance(BalanceRequest.defaultInstance());
  }
It first sleep to the next balance plan start time. Meanwhile, throttling by the max number
regions in transition to protect availability.
@param nextBalanceStartTime   The next balance plan start time
@param maxRegionsInTransition max number of regions in transition
@param cutoffTime             when to exit balancer
hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java