Fixes #8478 - set the version of mongodb we are using

The new version puppet-mongodb module expects the version of mongo to be
passed explicitly thought the globals. Load the available version via a custom
fact, as the version might differ on different platforms.
repoquery is not available on all machines and rpmquery only works on already installed packages. I think the current code will assume a pre-2.6.5 version but that may not be true.