Acceptance Tests: allow "Per VM" tests

[dduportal]

• Acceptance test harness is aimed at testing Puppet roles. Which should be done automaically (Bring back automated acceptance testing for roles #2248 and Bring back the Acceptance Test Harness #2249 )
• Infra team should be able to test "per node", e.g. allowing Vagrant to spin up a "copy" of the production node (or at least a node that is as close as possible) to increase the trust in changes.
  • We could bring back the staging branching model from a few years ago, as set up by Tyler and Olivier alternatively.