awsSpot: Batch boot requests
awsSpot: Batch boot requests

This patch changes awsSpot to batch its boot requests instead of
making a separate request for each machine one by one.  This should,
hopefully, prevent AWS from complaining about our request rate.

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