wish: automatic bootstrapping

[tv42]

Having a special node that needs to be started without -a, but only once, makes automation painful. Every doozerd should be able to always be started with a -a listing all the other doozerd nodes, and they should be able to figure out bootstrapping by themselves. (Though this may require persistency.)

In an earlier project called Ceph, that uses Paxos for cluster state, we solved this by letting admin list "seed nodes", and a cluster would bootstrap once a quorum of those seed nodes was willing to agree on bootstrapping: http://ceph.com/docs/master/rados/configuration/mon-config-ref/#initial-members . This lets Ceph do e.g. automatic deploys with 7 monitors, let them come up at any time, and when they're ready, they reach quorum. No human intervention!