Fix for crash when generating the nodelist.xml file

[azeno]

Hey vux!

I just stumbled upon this when generating our nodelist.xml file. I had your pack installed and on vvvv shutdown I got a very nasty ExecutionEngineException. By waiting on the scheduler thread to terminate gracefully the exception did not occur again.

All the best, Elias

[mrvux]

thinking about it, I guess should actually completely wait for end (without arbitrary timeout).

So join() would make more sense even

[mrvux]

Merging, thanks, I'll move timeout