Puppet provisioner

This uses:

- Puppet repo parallel to this dir.
- Extdata from development repo, per previous dev VM.

It throws out a lot of warnings about Ruby scoping and deprecations, and
Puppet storeconfigs, so we might decide not to use this.
Override govuk_class and govuk_platform

Set these two Facts via temporary environment variables. `govuk_class` comes
from the JSON node definitions. `govuk_platform` is currently hardcoded to
`development` in order to match some manifest conditions from the previous
VM - including the location of extdata.