(PUP-3016) Use the puppet() helper instead of assuming it is in $PATH

Use the puppet() helper function instead of assuming puppet is in the path. After installing puppet on a Windows system in particular, it's path is not reflected in the shell environment. Using puppet() lets Beaker figure out how to execute the puppet binary.
is it important to be testing with the "--version <#{module_version}"  functionality here?  looks like it was removed