synchronized boolean tryRunnable() {
    // Don't use isWaiting in the below; it returns true for WAITING and WAITING_TIMEOUT
    if (getState() == ProcedureState.WAITING && childrenCountDown()) {
      setState(ProcedureState.RUNNABLE);
      return true;
    } else {
      return false;
    }
  }
Try to set this procedure into RUNNABLE state. Succeeds if all subprocedures/children are done.
@return True if we were able to move procedure to RUNNABLE state.
hbase-procedure/src/main/java/org/apache/hadoop/hbase/procedure2/Procedure.java