Key for key in dool_disk_avgqu.py to avoid KeyError

[Flowdalic]

Running "make test" may fail with:

Traceback (most recent call last): File "./dool", line 2899, in main() File "./dool", line 2751, in main scheduler.run() File "/usr/lib/python3.7/sched.py", line 151, in run action(*argument, **kwargs) File "./dool", line 2847, in perform o.extract() File "", line 63, in extract KeyError: 'rq_ticks' make: *** [Makefile:38: test] Error 1

See https://bugs.gentoo.org/784704