Temporary fix to make steps with no host-driven tests pass.

Currently steps with no host-driven tests are marked as failure because
no tests are found.

NOTRY=True
BUG=

Review URL: https://chromiumcodereview.appspot.com/22267011

git-svn-id: http://src.chromium.org/svn/trunk/src/build@215986 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/pylib/base/test_dispatcher.py

@@ -363,7 +363,7 @@ def RunTests(tests, runner_factory, wait_for_debugger, test_device,
   """
   if not tests:
     logging.error('No tests to run.')
-    return (base_test_result.TestRunResults(), constants.ERROR_EXIT_CODE)
+    return (base_test_result.TestRunResults(), 0)
 
   if shard:
     # Generate a shared _TestCollection object for all test runners, so they