Update vagrant box to 20140829
Update vagrant box to 20140829

I have updated our Vagrant boxes to 20140829, which is based on Ubuntu
12.04.5 with the latest lts-trusty kernel. We should use this.

I've tested it - the jumpbox comes up fine (it's already been tested
against the full dev VM).

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