Dedupe Vagrantfile for v1/v2 usage
Dedupe Vagrantfile for v1/v2 usage

Personally I'd rather just bin off v1 support and make everyone upgrade. But
for the meantime DRY up some of the code that supports method and argument
naming in either version. This should prevent me editing one line and then
forgetting that I'm actually using the one below.

Tested on Vagrant 1.0.7 - seems to work fine.

alphagov/ci-puppet,boffbowsh/ci-puppet,boffbowsh/ci-puppet,alphagov/ci-puppet,boffbowsh/ci-puppet,boffbowsh/ci-puppet,alphagov/ci-puppet,alphagov/ci-puppet