Make the Jenkins build fail when it encounters errors at any step
Make the Jenkins build fail when it encounters errors at any step

- I had some test errors (not failures) in a branch:
  ```
  472 runs, 756 assertions, 0 failures, 2 errors, 1 skips
  [...]
  rake aborted!
  Command failed with status (1):
  [/usr/lib/rbenv/versions/2.1.8/bin/ruby -I"...]```.
  Jenkins wasn't exiting at that point, it was carrying on to do the
  rest of the tasks and eventually exited with `SUCCESS`.

alphagov/gds-api-adapters