Enable multiple clients for memtier

[slice4e]

The ability to run multiple-clients
-Currently a hacky way is to launch 2 versions of the script.
-There are problems with that - e.g. one script can try to kill the redis-servers of the other etc.

Solution 1: 
	Capture PIDs of redis servers to kill. This is a temporary fix, so that you can launch multive copies of the script. 
Solution 2:
	Enable multiple-clients in the config file and scripts. List the IPs of the clients in the config file.