Updates Pupetfile

Adds capability to ooverride settings by placing
a custom Puppetfile in the builder_overrides directory.

This allows us to trim this file down to the bare essentials
required to install base openstack.
Update vagrantfile

- for compat with vagrant V2
- to allow external nodes to be defined by vendors
Embed hiera into manifest

B/c otherwise you have to deal with another
directory. It's a lot of fuss for such a tiny
bit of config.
Ensure that override files are ignored

They are intended to be copied in after this repo
is cloned, but not commits into it.