support :public_network and writable issue

[luanntvn]

writable issue: on MacOSX (mine is 10.6.8), we can assign write permission with ACL extensions, like: sudo chmod +a "$USER allow write,append" /etc/hosts, but File.writable returns false while File.writable_real returns true

[rheinardkorf]

Awesome patch thanks.

Could the contributors please look at merging this?

For others who stumble upon this, you will need to add a static IP to your public network settings in Vagrantfile.

e.g.
config.vm.network "public_network", ip: "192.168.1.20", bridge: 'en1: Wi-Fi (AirPort)'

Of course, update with your IP and your network interface (the example is the standard bridge interface on OSX).

[devnix]

Right now, working like a charm on Ubuntu 14.10. I guess I will test it soon on Elementary Isis 😄

config.vm.network "public_network", ip: "192.168.1.50", :bridge => 'wlan0'

Please, consider merging this!

[mbarcia]

Also, please consider merging this, thank you

[cgsmith]

Merged with develop