gpu_test: subprocess.CalledProcessError: Command 'wmctrl -l | grep glxgears' returned non-zero exit status 1

PythonArgs: ['/usr/share/checkbox/scripts/gpu_test']
Traceback:
 Traceback (most recent call last):
   File "/usr/share/checkbox/scripts/gpu_test", line 216, in <module>
     sys.exit(main())
   File "/usr/share/checkbox/scripts/gpu_test", line 160, in main
     shell=True)
   File "/usr/lib/python3.3/subprocess.py", line 586, in check_output
     raise CalledProcessError(retcode, process.args, output=output)
 subprocess.CalledProcessError: Command 'wmctrl -l | grep glxgears' returned non-zero exit status 1

This is using :

# dpkg --list checkbox plainbox
||/ Name Version Architecture Description
+++-======================-================-================-=======
ii checkbox 0.16.8+bzr2319+2 amd64 System testing application
ii plainbox 0.3+bzr2322+bzr1 all Simple replacement for CheckBox

and what I did was run plainbox sru on this system.

This is similar to bug 1172851, but since that one is already fix-released, it's potentially not the same problem.

Part of the impact I'm seeing is that plainbox testing stalls, and the glxgears and video-playing firefox remain there.

Maybe we could have gpu_test catch CalledProcessError and recover gracefully.