(OPS-4195) Reduce pinning on puppet labs' apt repo

The 900 pin on the puppet labs' apt repo is a bit excessive. Since apt
defaults to a pin of 500 for repos, so anything over 500 should be
sufficient to prioritize our packages. This commit updates it to 550,
which leaves more room for other repos to pin above this as needed.
Merge pull request #5 from haus/ticket/master/ops_4195_reduce_apt_pin

(OPS-4195) Reduce pinning on puppet labs' apt repo