[ios] Updates run.py to accept --host-app.

The bot recipe is now passing this flag, and run.py passes unrecognized
flags along to the app under test. Some test apps fail when passed
invalid flags, so have the run.py script accept and ignore --host-app to
prevent it from being passed along to the app under test.

BUG=939373

Change-Id: Ie4b2456c19e96653b30b241fef958c27ede89228
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1611900
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659502}

ios/build/bots/scripts/run.py

@@ -147,6 +147,12 @@ def parse_args():
     metavar='app',
     required='-x' not in sys.argv and '--xcode-parallelization' not in sys.argv,
   )
+  parser.add_argument(
+    '--host-app',
+    help='Compiled host .app to run.',
+    metavar='host_app',
+    required='-x' not in sys.argv and '--xcode-parallelization' not in sys.argv,
+  )
   parser.add_argument(
     '-b',
     '--xcode-build-version',