bug 1402950: Add Chrome to integration tests
bug 1402950: Add Chrome to integration tests

* Add Google Chrome to the integration test suite. In our selenium 2
  version, this is Chrome 47, released December 2016.
* Run Chrome, Firefox, and headless (requests) tests in parallel
* Run parallel functionaltests equal to the number of selenium nodes
* Manually create and stop containers, to avoid a bug in auto-stopping
  containers in dockerRun
* Re-run tests on failure, to deal with flakiness of low-usage
  infrastructure like staging
* Be doubly verbose
* In several runs, a chrome node would become unresponsive, and the
  test would hang forever. Timeout the pytest run in 4 minutes,
  and enforce a Jenkins timeout of 5 minutes.
* Notify IRC on tests success or failure

SphinxKnight/kuma,SphinxKnight/kuma,Elchi3/kuma,a2sheppy/kuma,a2sheppy/kuma,mozilla/kuma,a2sheppy/kuma,jwhitlock/kuma,jwhitlock/kuma,escattone/kuma,mozilla/kuma,a2sheppy/kuma,jwhitlock/kuma,mozilla/kuma,Elchi3/kuma,Elchi3/kuma,mozilla/kuma,SphinxKnight/kuma,SphinxKnight/kuma,jwhitlock/kuma,escattone/kuma,Elchi3/kuma,jwhitlock/kuma,SphinxKnight/kuma,escattone/kuma,SphinxKnight/kuma,mozilla/kuma,Elchi3/kuma,a2sheppy/kuma