@Override
    public void start(int numThreads) throws IOException {
      this.numThreads = numThreads;
      setRunning(true);
    }
Testcase for HBASE-28210, where we persist the procedure which has been inserted later to
{@link RootProcedureState} first and then crash, and then cause holes in stack ids when loading,
and finally fail the start up of master.
hbase-procedure/src/test/java/org/apache/hadoop/hbase/procedure2/TestStackIdHoles.java