protected List<ServerName> selectServers() throws IOException {
    return Arrays.asList(getCurrentServers());
  }
Gracefully restarts every regionserver in a rolling fashion. At each step, it unloads, restarts
the loads every rs server sleeping randomly (0-sleepTime) in between servers.
hbase-it/src/test/java/org/apache/hadoop/hbase/chaos/actions/GracefulRollingRestartRsAction.java