Refactor Puppet Installation and fix DS-1681 (also seemingly fixes personal GitHub fork issues)

This PR makes several minor changes:

1. Refactors the DSpace Puppet scripts slightly, such that they hardcode less default values
2. Add additional comments to the Puppet scripts to explain what they are doing. Cleanup whitespace.
3. Move the PSI Probe install process to the 'dspace-init.pp' script (It's not really part of installing DSpace, so it shouldn't be in the "dspace::install" script)
4. Finally, fix DS-1681 as described in that JIRA ticket: https://jira.duraspace.org/browse/DS-1681

As a side-effect of the refactoring work, the problems with being able to change the "git_repo" to a personal GitHub fork seem to be RESOLVED. Previously, sometimes there would be odd issues if you wanted to run 'vagrant-dspace' using your own personal GitHub repo (e.g. tdonohue/DSpace on GitHub in my case).