(#201) Use root to exec

User root is needed to execute this command.

If someone changes the default Exec user, apt-add-repository will fail.
Change - to _

I did it to please my syntax validator, but I'm assuming it wasn't functioning as expected either.
Merge pull request #205 from braddeicide/master

fixed include, contained dash instead of underline.
Merge pull request #202 from tsuharesu/bug/exec_apt_ppa_as_root

Apt::ppa should exec with root
Convert existing tests over to beakr-rspec.
Merge pull request #206 from apenney/beaker-rspec

Convert existing tests over to beakr-rspec.