Stop auto-upgrading Jenkins (envinject broken)
Stop auto-upgrading Jenkins (envinject broken)

Per the inline FIXME comment. I've downgraded `ci.alphagov` as follows:
```
dcarley@production-management:~$ sudo dpkg -i jenkins_1.520_all.deb
dpkg: warning: downgrading jenkins from 1.521 to 1.520.
```

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet