minion/etcd: Lower log level when failing to create the minion dir
minion/etcd: Lower log level when failing to create the minion dir

The tester was failing because we were logging a warning when etcd
failed to create the minion dir a few times at boot. This is
expected, so it should only log an debug level message.

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