PUP-3155 Improve spec tests around the PE puppet version

Before this commit, when checking the puppet version on a PE build,
several characters; '(', ')' and '.'; caused problems with the regex.
This commit Regexp.escape-s them.
Merge pull request #3031 from andersonmills/fix/master/PUP-3155-improve_pe_version_spec_tests

PUP-3155 Improve spec tests around the PE puppet version