Fix presubmit check with newer version of AppEngine SDK v1.7.6.

The kill() call may fail because the process already exited.

TBR=iannucci@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/13867008

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@194126 0039d316-1c4b-4281-b951-d872f2087c98

testing_support/local_rietveld.py

@@ -139,7 +139,10 @@ class LocalRietveld(object):
 
   def stop_server(self):
     if self.test_server:
-      self.test_server.kill()
+      try:
+        self.test_server.kill()
+      except OSError:
+        pass
       self.test_server.wait()
       self.test_server = None
       self.port = None