Resolved FABRIC-624 - fixed process manager ProcessControllerTest

Hi,

Last night I've fixed race condition [1] in `ProcessUtils#killProcess` that basically resolved problems with `ProcessControllerTest`. I also applied my process testing API [2] to that test, to make it smaller and to be sure that spawned process is properly killed (i.e. not leaking on build machine).

Cheers.

[1] https://github.com/fabric8io/fabric8/pull/1455
[2] https://github.com/fabric8io/fabric8/pull/1453