processgroup: change the polling interval for killProcessGroup()

to make the function faster on average. Since killing a process
takes about 40-60ms on a recent device, the previous logic tends
to sleep too long. This CL does not significantly change the total
timeout (old code: 204ms, new code: 200ms).

Bug: 21813611
Change-Id: Ica44b2437ccccaebadcf585d7a09d993ce71a499
1 file changed