Remove old `forward_port` method for configuration. Use `network`
Booting new VirtualBox VM should check for port collisions
Explicitly set error handling for port collision on resume
Remove network validation on config. We'll re-add this later.
VirtualBox forwarding port uses new `network` calls
Temporarily disable Network action while it is broken
Fix ordering of forwarded_port call
Rework v1 forward_port call to append forward port networks
New Network VirtualBox middleware to handle the changes.

Note this is a WIP (hence committed on a branch)
Check port collisions now uses the new high-level networking
Forwarded ports use the new high-level configuration
Configure networks on the VM
Add support for bridged networks again
Support mac address and nic_type for host only networks
Remove the old networking code
Util::ScopedHashOverride
Use scoped hash overrides for high-level config
Forwarded ports allow for scoped hash overrides
Raise proper error if there aren't any NIC slots available
Merge branch 'abstract-networks'

This introduces the new network configuration syntax for Vagrant 1.1
and forward.

== The Problem

With multiple providers, the concept of networking as it stands in Vagrant
1.0.x becomes really muddy. We have `config.vm.forward_port` and
`config.vm.network :hostonly` and `config.vm.network :bridged`. But what
if someone writes an AWS provider? What is a bridged network in AWS? It
just doesn't make sense.

Networking working out of the box with Vagrant is a core part of what
makes Vagrant "magic" to new users. It is a core part of what makes Vagrant
simple to use. One option to punt networking to provider-specific
configuration was considered, but I found the whole idea of networking
too core to Vagrant to simply punt.

Because of this, a whole new method of networking is introduced.

== The Solution

The solution is to have a high-level notion of networking for Vagrant
configuration. This should cover the most _common_ cases of networking, and
every provider should do their best to implement these high-level
abstractions, to ensure the "just works" nature of Vagrant.

In addition to this high-level networking, low-level networking options
should be exposed on the provider configuration. This allows users to do
advanced provider-specific networking configuration if they want, but aren't
required to.

== High-Level Abstractions

=== Available Types

The high-level abstractions built into Vagrant will be the following:

* Forwarded ports - A mapping of host port to guest port that one can hit
  using `localhost`.
* Private network - A private network, the machine should ideally be
  protected from public access.
* Public network - A public network, one that is easily accessible by
  others.

I'm not sure if these are the proper abstractions. They can change up
until 2.0, but these are what we have so far.

Theoretically, here is how mappings would work. Note that this is just
an example, and the mappings in practice of such providers may or
may not map to this as follows.

**VirtualBox**
* Forwarded ports - NAT network, forwared ports.
* Private network - Hostonly network, static IP assigned.
* Public network - Bridged network, IP assigned via DHCP from router.

**VMWare**
* Forwarded ports - NAT network, forwarded ports.
* Private network - Hostonly network, static IP assigned.
* Public network - Bridged network, IP assigned via DHCP from router.

**AWS**
* Forwarded ports - Unimplemented.
* Private network - Public DNS in EC2, private IP in VPC.
* Public network - Elastic IP in EC2 and VPC.

=== Syntax

Networks are configured at the top-level of a Vagrantfile:

```ruby
Vagrant.configure("2") do |config|
  # ...

  config.vm.network :forwarded_port, 80, 8080
  config.vm.network :private_network, "192.168.1.12"
  config.vm.network :public_network
end
```

Providers should do their best to honor these configurations.

=== Advanced Options

While providers should do their best to satisfy the requirements for the
high-level abstractions, it is expected that provider-specific configuration
may be possible per network, even for the high-level configurations. For
this, provider-prefixed configuration options should be done:

```ruby
config.vm.network :forwarded_port, 80, 8000,
  :vmware__device => "vmnet8"

config.vm.network :public_network,
  :aws__elastic_ip => "1.2.3.4",
  :vmware__device => "en0"
```

If at all possible, providers should **not** require advanced options for
these to function.

== Low-level Configuration

While the high-level configuration should satisfy the common case and make
Vagrant work out of the box for most providers, one of the large benefits of
many providers is the ability to do certain networking tricks. For example,
KVM, Hyper-V, vSphere, etc. can create and be a part of true VLANs, which
may be required for certain upstream networking rules/ACLs. For things like
this, the network configuration should go directly into the provider
configuration in some way.

Examples:

```ruby
config.vm.provider :virtualbox do |vb|
  vb.network_adapter 2, :hostonly
  vb.network_adapter 3, :nat
end

config.vm.provider :aws do |aws|
  aws.routing_table = "route-123456"
end
```

It is up to the provider implementation to define the configuration
syntax as well as the implementation details of such an option. Other
providers are unable to see provider configurations other than their own
so it is truly private to the provider.