[Telemetry] Fix run_test return code.

BUG=

Review URL: https://codereview.chromium.org/11788006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@175251 0039d316-1c4b-4281-b951-d872f2087c98

tools/telemetry/telemetry/run_tests.py

@@ -140,4 +140,4 @@ def Main(args, start_dir, top_level_dir):
     os.chdir(olddir)
     options_for_unittests.Set(None, None)
 
-  return max(num_errors, 255)
+  return min(num_errors, 255)