QA: Using the new way of starting a custom browser

mediawiki_selenium Ruby gem is now able to start local and remote
browsers with optional browser setup. Removed NEARBY_FIREFOX support.

Paired with Kartik Mistry, Chris McMahon.

Bug: 62512
Change-Id: Idb2cd0277278f85506273f80c3c975bc7db9f010
Merge "QA: Using the new way of starting a custom browser"