Highly limited osx (darwin) guest plugin.

- Tested on mountainlion/virtualbox
- virtualbox shared folders will not work (no vboxvsf support)
- Must use at least 2GB of RAM or the os will refuse to boot(mountainlion requirement)

To begin, create a mountainlion vm in virtualbox. You will need to install from scratch most likely, and assign at least 2GB of ram for it to install.

Create 2 network interfaces, the first one a NAT interface, second a hostonly interface.

'vagrant package' the VM.

In your vagrant file, be sure that the synced folder is disabled:
config.vm.synced_folder "vagrant", "/vagrant", disabled: true
Working implementation with NFS, still some caveats:
- There's a lengthy sleep in there, probably could use a back-off loop
- en1 seems totally worthless on vbox, I skip it and just use the en2 it creates.
Change mount_nfs_folder cap to be more like the linux version, adding a
bunch of retires rather than a long sleep.

Add DarwinNFSMountFailed error. This might move be more appropriate at
the plugin level.

Integrate some of tvsutton's work in configure_networks to get the
implementation closer to working in both fusion and virtualbox.

Add shell_expand_guest_path capability (also copied from linux)
Tabs must die.
Remove the +1 offset, I resolved the issue with the 'phantom' en1
interface. For some reason interfaces still skip en1, but provided we
enumerate based on order and not name, things should work smoothly.
Darwin guest: mount_vmware_shared_folder cap for use with vmware_fusion provider

- It's not clear whether it's possible to mount individual shares
  using 'mount -t vmhgfs', as the vagrant-vmware-fusion provider now does
  for Linux guests. Any mount from '.host', even if not a valid share
  name, succeeds and mounts _all_ shares in their respective directories
  at the root of the mountpoint. Instead, we symlink each directory from
  its place in '/Volumes/VMware Shared Folders'
Darwin: clean up temporary network interface file downloaded from guest
Update Darwin guest description
Darwin: code debug cleanup
Darwin: use :sudo for communicate.test
Merge pull request #1914 from b2jrock/darwin-guest

OS X (darwin) guest support.