testrunner: Kill whole process group on timeout.

This avoids occasional deadlocks of the python script.

It seems that proc.communicate will not return until all children exit
(possibly because it is waiting for end-of-file from the shared PIPE).

Bug: 140933800
Bug: 141227454
Test: test.py -b -r --gcstress --jit --host --64
Change-Id: Ie230ab100a092a920bdbcb1c3bb50e493572562a
1 file changed