naggen2: remove ensure_resource

In puppet 2.7, resources declared with ensure_resource will NOT be found
by 'require' clauses; in puppet 3 the dependency is correctly honored,
on the other hand. Reverting to package resources so that this works
cross-versions.

Change-Id: Ie6bcfb53d47a3c6bdaafb34f74e0bf5eeff314e5
Signed-off-by: Giuseppe Lavagetto <glavagetto@wikimedia.org>