tweak operations-dns-lint

Faidon wrote the authdns::lint class in puppet which provides a shell
script to lint the operations/dns.git checkout.
https://gerrit.wikimedia.org/r/#/c/82264

That requires the label hasContintPackages (ie the production
contint::packages manifest is applied on the slave).

Change-Id: I2d418cee9f1d97b8d470de4af2bb6e224525d840