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.
We found success in removing the private_network value from the inner Vagrantfile and just moving it to the outer one, which would make it look like the following:

```ruby
Vagrant.configure('2') do |config|
  config.vm.box = 'bosh-lite-ubuntu-trusty'

  config.vm.provider :virtualbox do |v, override|
    override.vm.network :private_network, ip: '192.168.54.4'

    #CDN in front of bosh-lite-build-artifacts.s3.amazonaws.com
    override.vm.box_url = 'http://d3a4sadvqj176z.cloudfront.net/bosh-lite/latest/bosh-lite-virtualbox-ubuntu-14-04-0.box'
  end

  [:vmware_fusion, :vmware_desktop, :vmware_workstation].each do |provider|
    config.vm.provider provider do |v, override|
      override.vm.network :private_network, ip: '192.168.50.4'
    end
  end
end
```