Sudo support

This adds support for a sudo, sudo_users, and sudo_group option to Mixlib::ShellOut. If you enable it, it will automatically prepend sudo to the command you are about to run. 

It takes absolutely no precautions for feeding passwords *in* to sudo, not hanging you by the neck if it's not configured, or anything else for that matter.

Another PR coming in to Chef for a sudo metaparam.