@RestrictedApi(explanation = "Should only be called in tests", link = "",
      allowedOnPath = ".*/src/test/.*")
  Set<ServerName> getParsedServers() throws IOException {
    return FutureUtils.get(rpcStubHolder.getStubs()).keySet();
  }
send requests concurrently to hedgedReadsFanout end points. If any of the request is succeeded,
we will complete the future and quit. If all the requests in one round are failed, we will
start another round to send requests concurrently tohedgedReadsFanout end points. If all end
points have been tried and all of them are failed, we will fail the future.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AbstractRpcBasedConnectionRegistry.java