Implement forceful termination of launched CLI after a timeout in Java ProcessUtils.

[st]

Implement forceful termination of launched CLI after a timeout in Java ProcessUtils (connector).
If CLI doesn't respect provided timeout, (and goes zombie), Java side should kill this process.

[konstan]

This is where change should happen https://github.com/slipstream/SlipStreamServer/blob/master/jar-connector/src/main/java/com/sixsq/slipstream/util/ProcessUtils.java#L72

The problem here is to obtain the timeout the CLI was started with. Might need to update the signature of some of execGetOutput*() methods to explicitly require the timeout. If the CLI didn't return after timeout + (say) 2 sec - kill it with a system call and report back the collected std/err outputs.