Puppet 3.5.0 introduced strict variables and the module handles strict
variables by using the defined() function. This does not work on prior
versions of puppet so we must gate based on that version.
Puppet 4 series has a new setting `strict` that may be set to enforce
strict variables while `strict_variables` remains unset (see PUP-6358)
which causes this conditional to erroniously use non-strict 3.5-era
parsing and fail.
The new conditional corrects the cases such that strict variable
behavior happens on versions 3.5.0 and later.
