Remove provider config from main Vagrantfile and embed inside box

This is a proposal for a different way of dealing with provider specific aspects of the bosh-lite vagrant boxes.  Instead of having all of the logic inside of the main `Vagrantfile`, move it into the box file proper.  This greatly simplifies the contents of the main `Vagrantfile` and removes the need for end users to specify a "machine" configuration name.  This style of build is also very well suited for the versioning support and update checks provided by vagrant cloud.

The environment variables that influence the provider config are still honored.  Provisioner scripts in the aws box have been assigned id's so they can be overridden or disabled by the box user.  Configuration that exists in the user's project `Vagrantfile` takes precedence over what's in the box.

I've also made some changes to clean up the messages that are issued when bringing up an aws image and make the aws script provisioners that dump the IP and add routing rules run always.

https://asciinema.org/a/11799 should give an idea of what things look like with these changes.
Given that the private_network is defined in the template, now used by Packer, how do we override this value in the outer Vagrantfile (the one at the root of the bosh-lite directory)?

This comes up as an issue when we're developing boxes as we tend to bring up multiple boxes at once across VMWare and Virtualbox. Previously we'd just change the private_network value from x.x.50.4 to x.x.54.4 or something, but doing so in the outer Vagrantfile didn't seem to have an effect.