[QA] [Update] Browser tests per patch

[Jon Robson]

Background: mobile wants to gain more confidence in its browser tests
by running a subset of browser tests on a case by case basis [0].

Good news: I've got a proof of concept running and Barry the browser
test bot has given some legitimate helpful reviews to Gather [1].

Even better news: It's proving itself valuable already [2].
As you can see in the messages the bot has posted on [3] we have a
couple of options on display option format for his reviews.

So.. hopefully this short experience has sold you all already.

This script is currently a manual job and needs a bit of tweaking
before we can put it in a cron job/run it always - it needs to watch
for new commits and then run a modification of the above script on a
per case basis (if two versions of it run in parallel we have an
issue).

Definitely something we should push for next sprint!

Long live Barry bot!

Devs... (everyone else now of what follows is likely to be useful):
I got the labs instance up and running on:
http://gather-browser-tests.wmflabs.org/wiki/Main_Page

Most of you in readership team should be able to ssh
gather-browser-tests.eqiad.wmflabs
Let me know if you have no access.

It's currently working via a script that you can find here:
/srv/mediawiki/extensions/Gather/tests/browser/Barry.sh

[0] https://phabricator.wikimedia.org/T100293
[1] https://gerrit.wikimedia.org/r/#/q/reviewer:jdlrobson%252Bbarry%2540gmail.com+status:open,n,z
[2] https://gerrit.wikimedia.org/r/#/c/218731/