Fixed login method, instead of waiting for link with text in English, wait for link with href

Paired with Amir Aharoni.

Longer error message: timed out after 5 seconds, waiting for
{:text=>"Log out", :tag_name=>"a"} to become present
(Watir::Wait::TimeoutError)

Example job:
https://wmf.ci.cloudbees.com/view/uls/job/UniversalLanguageSelector-lang
uage-browsertests.wmflabs.org-linux-firefox/lastCompletedBuild/testRepor
t/(root)/Font%20selection/Font_selector_pane_appears/

Change-Id: I722b90272b1f3c56fc0a46b920212f79a37fdb8a