db: Minor style tweak
db: Minor style tweak

This patch changes the less() function in db/machine.go to use
db.Master instead of the string "Master" directly.  Slightly more
future proof.

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