Use shared `buildProject` task in CI
Use shared `buildProject` task in CI

Use the common jenkinslib build task to build the project. This improves
performance by fixing job throttling, and means that static will share
any future build improvements.

Override the test task so that the Ruby and JS tests are run separately.
Running them in same default rake task causes confusing test errors:
http://stackoverflow.com/questions/26235828/actionviewtemplateerror-wrong-number-of-arguments-3-for-1-2

alphagov/static,alphagov/static,alphagov/static