look for the enable/disable/accept/reject commands in multiple directories with and without the cups prefix

This is my first-ever pull request, so don't hesitate to point out all the things I've likely done incorrectly.

I'm also not very proficient with ruby, so stylistic and idiomatic changes are likely needed.

The basic idea is to not hardcode the paths to the binaries, instead searching for them in several possible locations, but with and without the "cups" prefix.  First one found wins.

There's no case that handles what happens if none are found.  That should probably be fixed.

Looking at some of the other providers that come with puppet 2.7.x, several of them don't use full paths to commands, they just use the command basename, e.g. "rpm".  That might be worth considering as an alternate approach.