dns: Log less aggressively if missing self minion
dns: Log less aggressively if missing self minion

When the minion first boots, the self minion doesn't exist and the DNS
module was warning.  This is expected behavior, so a warn is too
aggressive.  This patch downgrades the log level to Debug.

NetSys/quilt,stevenlin598/quilt,kklin/quilt,kklin/quilt,PenguinToast/quilt,PenguinToast/quilt,mmussomele/quilt,ejj/quilt-dev,stevenlin598/quilt,stevenlin598/quilt,tejasmanohar/quilt,kelda/kelda,kklin/kelda,quilt/quilt,kayousterhout/quilt,LuiseV/quilt,LuiseV/quilt,kelda/kelda,kklin/kelda,NetSys/quilt,LuiseV/quilt,PenguinToast/quilt,mmussomele/quilt,stevenlin598/quilt,mmussomele/quilt,kklin/quilt,ejj/quilt-dev,mmussomele/quilt,tejasmanohar/quilt,kelda/kelda,stevenlin598/quilt,quilt/quilt,LuiseV/quilt,stevenlin598/quilt,PenguinToast/quilt,mmussomele/quilt,NetSys/quilt,kayousterhout/quilt,mmussomele/quilt,ejj/quilt-dev,NetSys/quilt,quilt/quilt,LuiseV/quilt,tejasmanohar/quilt,ejj/quilt-dev,kklin/kelda,kklin/quilt,kklin/kelda,NetSys/quilt,tejasmanohar/quilt,PenguinToast/quilt,kayousterhout/quilt,kayousterhout/quilt,quilt/quilt,kelda/kelda