[QA] Test failures -> Trello: Introducing Sellello

[Jon Robson]

A new tool to add to the Bingle and Bugello family - introduce Selello

Selello checks the state of RSS feeds published by Jenkins relating to
failed browser tests e.g. this one for MobileFrontend[1]

When a browser test has been failing for a considerable time e.g. for
the last 3 builds it will post a card to Trello. No card will be
posted on the 4th or 5th time the tests fail.

An output card can be found here:
https://trello.com/c/BFoSR3XY/58-firefox-build-575-failing-selenium-tests


e.g. It will only post a card if
1) The current build is failing
2) The last build to pass was over 3 runs ago.

I'm hoping this will be a better alert mechanism than the current
notification emails.

Please help me get this reviewed and up and running! [2]


[1] https://wmf.ci.cloudbees.com/job/MobileFrontend-en.m.wikipedia.beta.wmflabs.org-linux-chrome/
[2] https://github.com/wikimedia/bingle/pull/38