Implement sorting of synced_folders
Implement sorting of synced_folders

It's useful if you want to mount something inside /vagrant or if you
have some another mount in some synced folder.

This piece of code is extracted from virtualbox driver.

kevinlowrie/vagrant-lxc,ccope/vagrant-lxc,danielhodder/vagrant-lxc,danielhodder/vagrant-lxc,globin/vagrant-lxc,ccope/vagrant-lxc,globin/vagrant-lxc,fgrehm/vagrant-lxc,spheresh/vagrant-lxc,danielhodder/vagrant-lxc,ccope/vagrant-lxc,globin/vagrant-lxc,mayflower/vagrant-lxc,mayflower/vagrant-lxc,Val/vagrant-lxc,necrose99/vagrant-lxc,Val/vagrant-lxc,Val/vagrant-lxc,fgrehm/vagrant-lxc,spheresh/vagrant-lxc,kevinlowrie/vagrant-lxc,necrose99/vagrant-lxc,kevinlowrie/vagrant-lxc,mayflower/vagrant-lxc,fgrehm/vagrant-lxc,spheresh/vagrant-lxc,necrose99/vagrant-lxc