Turn the mac3 build red when tests fail.

buildbot/master/master.cfg

@@ -168,8 +168,8 @@ mac3_factory.addStep(Git(repourl=SERVO_REPO, mode="full", method="clobber"))
 mac3_factory.addStep(Compile(command=["./mach", "build", "--dev"], env=mac_test_env))
 mac3_factory.addStep(ShellCommand(command=["./mach", "test-css", "--processes", "4",
                                            "--log-raw", "wpt_raw.log"],
-                                  env=mac_test_env, decodeRC={0:SUCCESS,
-                                                              1:SUCCESS},
+                                  env=mac_test_env,
+                                  haltOnFailure=False, flunkOnFailure=False,
                                   logfiles={"wpt_raw.log": "wpt_raw.log"}))
 
 android_compile_env = dict({'ANDROID_SDK': '/home/servo/android-sdk-linux/',