scheduler: Pull container boots outside the transaction
scheduler: Pull container boots outside the transaction

We had temporarily moved container boots into the scheduler database
transaction as a hack to reduce the parallelism between booting and
networking containers.  This was in an effort to fix an occasional
docker daemon bug that was since fixed by commit
0907977 (docker: Stop using docker exec).  Now that the fix has been
merged, we ca start slowly and carefully re-enabling the parallelism.

This patch should also fix a problem in which downloading large
containers freezes the minion long enough for it to be removed from
etcd.

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