skip chef/ruby checks

Hi,

Great project.

wanted to reduce a little noise, so added a configuration variable to skip the ruby/chef check.

Also noticed that the ruby check and the chef checks were setup differently.
install_ruby made the checks internally, while chef.install only happened when the external chef check didn't pass.

I made a stab for the external version, but please advise if you prefer the other way. I can change easily.
I liked the external because it reduced the amount of information going across the screen. But am unsure about your use case with the no_release flag

Thanks,
Keenan