Bug 943844 - [v1.2] Intermittent failures of test_browser_bookmark.py on Travis on v1.2

I reproduced this failure locally using b2g desktop. Sometimes they keyboard just doesn't appear when `sendkeys()` is called. I don't know why, and don't think that's necessarily a bug. This should fix the intermittent failures we are seeing, but I'm not sure if it's what we really want to do.

Looking for feedback.