adb: fix race condition in test_non_interactive_sigint.

Fix race condition in the test_non_interactive_sigint test by
looping for a while.

Bug: http://b/32336914
Test: python test_device.py
Change-Id: Ie65a762ad6f04815231add5444762c4c0ffd31cb

adb/test_device.py

@@ -473,8 +473,12 @@ class ShellTest(DeviceTest):
         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."""