Use modulepath as base for package versions yaml path

Uses Puppet's modulepath variable to find path
to manifests/(centos|ubuntu)-versions.yaml in a
reliable method that works with custom modulepath
specified during puppet invocation.

Change-Id: I67d471a120506f8a182a7b5d2f7110f2c7ce27ce
Closes-Bug: #1346247
Merge "Use modulepath as base for package versions yaml path"