Enable webrtc_nonparallel_tests on iOS simulator

tools_webrtc/ios/tests/common_tests.json

 {
   "tests": [
     {
       "app": "apprtcmobile_tests",
       "xctest": true
     },
     {
       "app": "audio_decoder_unittests"
     },
     {
@@ skipping 15 matching lines @@
       "app": "system_wrappers_unittests"
     },
     {
       "app": "test_support_unittests"
     },
     {
       "app": "tools_unittests"
     },
     {
       "app": "voice_engine_unittests"
+    },
+    {
+      "app": "webrtc_nonparallel_tests"
     }
   ]
 }