Add idle timeout to memcached and hot rod servers.

Add an IdleStateHandler to memcached and hot rod servers so that idle connections can be closed automatically. This is necessary to handle error conditions such as cases where clients erroneously indicate the server that it needs to read 20 bytes but they only send 10 bytes. Without such handler, the server will carry on waiting for bytes forever. The handler will provide a defence mechanism for such cases.

The timeout will be configurable via the command line. Besides, clients wanting to do some connection pooling will require to configure this accordingly in the server. In other words, there's hardly any point in having servers configured with idle timeout of 30 seconds and clients closing connections after 60 seconds of idle time. These two should be aligned accordingly.