@RestrictedApi(explanation = "Should only be called in tests", link = "",
      allowedOnPath = ".*/src/test/.*")
  PoolMap<ConnectionId, T> getConnections() {
    return connections;
  }
Configure an hbase rpccontroller
@param controller              to configure
@param channelOperationTimeout timeout for operation
@return configured controller
hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/AbstractRpcClient.java