adb: fix race condition in test_non_interactive_sigint.

        self.device.shell(proc_query)

        os.kill(sleep_proc.pid, signal.SIGINT)

        sleep_proc.communicate()

        self.assertEqual(1, self.device.shell_nocheck(proc_query)[0],

                         'subprocess failed to terminate')

        # It can take some time for the process to receive the signal and die.

        end_time = time.time() + 3

        while self.device.shell_nocheck(proc_query)[0] != 1:

            self.assertFalse(time.time() > end_time,

                             'subprocess failed to terminate in time')

    def test_non_interactive_stdin(self):

        """Tests that non-interactive shells send stdin."""