command/sudoers: Use Vagrant's ruby for the sudoers file

This makes things work on systems that don't have a global ruby
installation in place and fix GH-289
command/sudoers: Remove Cmnd_Alias from sudoers file

Since the wrapper is versioned, we would end up having multiple `LXC`
command aliases, making `sudo` unusable:

```
>>> /etc/sudoers.d/vagrant-lxc-1-0-0-alpha-3-dev: Alias `LXC' already
>>> defined near line 2 <<<
sudo: parse error in /etc/sudoers.d/vagrant-lxc-1-0-0-alpha-3-dev near
line 2
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin
```