Improved sudo management

* Set the puppetrun sudo command to match the user specified using puppetrun_user parameter
* Only manage the sudo rules if both puppetca and puppetrun are enabled

This is a refactor of #101 

The spec tests fail on my desktop, could use second pair of eyes as it appears like it shouldn't be failing.
I noticed you do conditionally set the correct sudo lines in the file, but not here. I think it makes a lot of sense to not create puppetrun or puppetca lines if the user is not going to use it.