dell::openmanage: kill probable dependency cycle

We have a general puppet rule that packages depend on yum cache cleaning.
So we can't clean yum cache after installing a package that depends on that
yum cache cleaning. Anyway, it's fine if that plugin is disabled for the next
puppet run or user action. We don't need yum to clean its cache right now so
we can safely get rid of that notification.
Remove unused variable
Use latest default to download
Remove fact srvadminpkgcount
Remove fact isopenmanagesupported
Update/add headers
Avoid potential troubles with scope
Merge pull request #20 from mremy/make_module_usable

Make module usable