Puppet 4 for CentOS

[sunnz]

Hi,

I have added pull request #56 that updates CentOS scripts so that the latest Puppet 4 is installed from Puppet Collection 1 repository.

A few extra improvements:

• Unified all CentOS scripts, they all now have a minor difference and should be compatible with their respective RHEL derivatives.
• A better way to check if Puppet is installed. You can no longer rely on $PATH as puppet directory has changed in version and may not be available for root.
• Added symlinks to puppet so that they are always in $PATH.