fix failing unit tests on Ubuntu

I discovered that unit tests buildslave.test.unit.test_runprocess.TestPOSIXKilling.test_double_fork* fails for me on an Ubuntu 13.10 machine.

After digging around it turns out that PPID of orphaned proccess are not set to 1, when you are running code from GUI session. This breaks the runproccess double fork tests.

Here is my suggestion to fix that problem.