Ignore swarming arguments in low_bandwidth_audio_test.py

Needed because swarming adds --isolated-script-test-output and --isolated-script-test-perf-output

See for example:
https://chromium-swarm.appspot.com/task?id=39006c763bebf710

No-Try: true
Bug: chromium:755660
Change-Id: Iff9fb3441200f760c511a67211fbc4a1272717b4
Reviewed-on: https://webrtc-review.googlesource.com/6362
Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Commit-Queue: Edward Lemur <ehmaldonado@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20146}

audio/test/low_bandwidth_audio_test.py

@@ -54,7 +54,14 @@ def _ParseArgs():
   parser.add_argument('--android', action='store_true',
       help='Perform the test on a connected Android device instead.')
   parser.add_argument('--adb-path', help='Path to adb binary.', default='adb')
+
+  # Ignore Chromium-specific flags
+  parser.add_argument('--isolated-script-test-output',
+                      type=str, default=None)
+  parser.add_argument('--isolated-script-test-chartjson-output',
+                      type=str, default=None)
   args = parser.parse_args()
+
   return args