misc/android: forward SIGQUIT to the process running on the device
When a test binary runs for too long, the go command sends it a
SIGQUIT to force a backtrace dump. On Android, the exec wrapper
will instead receive the signal and dump its backtrace.
Forward SIGQUIT signals from the wrapper to the wrapped process
to gain useful backtraces.
Inspired by issuse 25519; this CL would have revealed the hanging
test directly in the builder log.