[EchoClient] overhaul the EchoClient.cpp

• Reconnect (close, new socket, connect) when the TCP connection is unexpectedly closed and count the reconnects
• Send echo messages carrying information: "client-id:iteration"
• Use a Client class holding a clients state instead of a pthread-style clientFunc
• Create the Client object in the client Fiber to use NUMA first-touch policy
• Reduce code duplication:
  • starting a new Client is now done with Client::startNew
  • latency measurement and error handling are moved from the clientIteration* functions in the Client::run function