void switchSnapshotCleanup(final boolean on, final boolean synchronous) throws IOException {
    if (synchronous) {
      synchronized (this.snapshotCleanerChore) {
        switchSnapshotCleanup(on);
      }
    } else {
      switchSnapshotCleanup(on);
    }
  }
Turn on/off Snapshot Cleanup Chore
@param on indicates whether Snapshot Cleanup Chore is to be run
hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java