On Vagrant 1.9+ plugin gems are installed into a different folder, their path
containing the ruby version. This updates the regular expression whitelisting
the pipework script to reflect this change.
Previously, we hardcoded to using the ruby binary in /opt/vagrant[..].
On some systems, this path is incorrect, so instead we use the
path of the interpreter that is executing the `vagrant lxc sudoers`
command.
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
```
Sudoers now creates a safe wrapper script that performs sanity checks on sudo :
* wrapper generated in /usr/local/bin (name includes version to allow multiple wrappers on the same system)
* sudoers command now generates a one-line file in /etc/sudoers.d
* SudoWrapper use the new wrapper
* Removed unused Config#validate method
