* [monotouch-test] Optionally ignore tests that show permission dialogs.
* [xharness] Add support for excluding tests that require permission dialogs.
* [xharness] Ignore introspection tests if we don't want permission dialogs.
Ignore introspection tests for now if we don't want permission dialogs, since
figuring out which API requires permissions is a tedious process (which we'll
eventually have to do though).