Amended facter pupperversion check to cope with Enterprise string

When Puppet Enterprise is installed, facter returns both Open Source & Enterprise versions which causes Gem::Version.new() to throw an error "malformed version number"
Example version string:
*puppetversion => 3.6.2 (Puppet Enterprise 3.3.2)*

As you've already got a dependency to puppetlabs-stdlib I've made a call to retrieve the is_pe Facter variable ( https://github.com/puppetlabs/puppetlabs-stdlib/blob/master/lib/facter/pe_version.rb ) to determine if we need to split the Open Source version number from the Enterprise. 

Tested with **puppet-python 1.7.15** & **stdlib 4.4.0**. Please feel free to amend and improve as necessary but this was blocking us installing your module on a Puppet Enterprise node.

Cheers, Jonathan