The 12/24 hour format ui tests have race condition issues.

why not add some logic on the marionette tests that actually checks if the `navigator.mozHour12` is not `null`?

all the views are currently calling the [`View#waitForDisplay`](https://github.com/mozilla-b2g/gaia/blob/master/apps/calendar/test/marionette/lib/views/view.js#L46-L48) maybe we should add this extra logic there (the one that makes sure we don't execute any code before the `navigator.mozHour12` is set) - or we should report a bug telling that `mozHour12` can cause race conditions...

I think it's pretty bad idea to change the source code into something that is not correct just to make the test pass.