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.
The way this should be done is to associate an id with the network as configured in the box file:

```ruby
Vagrant.configure('2') do |config|
  config.vm.network :private_network, ip: '192.168.50.4', id: :local
  config.vm.hostname='bosh-lite'

  config.vm.provider :virtualbox do |vbox, override|
    vbox.customize ['modifyvm', :id, '--memory', VM_MEMORY]
    vbox.customize ['modifyvm', :id, '--cpus', VM_CORES]
    vbox.customize ['modifyvm', :id, '--natdnshostresolver1', 'on']
    vbox.customize ['modifyvm', :id, '--natdnsproxy1', 'on']
  end

  [:vmware_fusion, :vmware_desktop, :vmware_workstation].each do |provider|
    config.vm.provider provider do |vmware, override|
      vmware.vmx["numvcpus"] = VM_CORES
      vmware.vmx["memsize"] = VM_MEMORY
    end
  end
end
```
Then, when you need to override it, you use the ID:

```ruby
Vagrant.configure('2') do |config|
  config.vm.define 'bosh-lite'
  config.vm.box = 'bosh-lite-ubuntu-trusty'

  config.vm.network :private_network, ip: '192.168.50.5', id: :local

  config.vm.provider :virtualbox do |v, override|
    #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
end
```

When you do that, vagrant configures the correct address in the vm:
```
$ vagrant ssh -c 'ifconfig -a'
eth0      Link encap:Ethernet  HWaddr 08:00:27:e1:57:40  
          inet addr:10.0.2.15  Bcast:10.0.2.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fee1:5740/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:583 errors:0 dropped:0 overruns:0 frame:0
          TX packets:420 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:63813 (63.8 KB)  TX bytes:57393 (57.3 KB)

eth1      Link encap:Ethernet  HWaddr 08:00:27:1e:53:67  
          inet addr:192.168.50.5  Bcast:192.168.50.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fe1e:5367/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:11 errors:0 dropped:0 overruns:0 frame:0
          TX packets:12 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:1084 (1.0 KB)  TX bytes:964 (964.0 B)
```

Override style configuration works just as well:
```ruby
Vagrant.configure('2') do |config|
  config.vm.define 'bosh-lite'
  config.vm.box = 'bosh-lite-ubuntu-trusty'


  config.vm.provider :virtualbox do |v, override|
    #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'
    override.vm.network :private_network, ip: '192.168.50.5', id: :local
  end
end
```
yields
```
$ vagrant ssh -c 'ifconfig eth1'
eth1      Link encap:Ethernet  HWaddr 08:00:27:a0:67:fa  
          inet addr:192.168.50.5  Bcast:192.168.50.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fea0:67fa/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:7 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:768 (768.0 B)  TX bytes:648 (648.0 B)

Connection to 127.0.0.1 closed.
```