ms: Attempt to stop all mobile/virtphy instances on exit

We leave mobile/virtphy running after the test. Attempt to gracefully
exit and kill all of them. I experimented with both os.setpgrp and the
prctl(PR_SET_DEATH_SIG) but that didn't improve the situation.

Change-Id: I6cec050db7d4c355fb6678b2d84309fbbe5587b3
1 file changed