Add vagrant user & ssh key to Training VM

This pull request adds a new class to default node declaration that will add the standard ssh key for vagrant to the training vms. I am not adding root here as that is [already handled](https://github.com/puppetlabs/puppetlabs-training-bootstrap/pull/113/files) for use in the fundamentals class. At the moment I am only doing this for the training VMs after a quick chat with @nfagerlund . There will be a followup pull request with a Vagrantfile for all of our classes configuration to aid local testing of the classroom environment.