Assert that paxos quorum is set

ipam/paxos/paxos.go

@@ -128,6 +128,9 @@ func max(a uint, b uint) uint {
 // simply a matter of gossipping a new proposal that supersedes all
 // others.
 func (node *Node) Propose() {
+	if node.quorum == 0 {
+		panic("Paxos node.Propose() called with no quorum set")
+	}
 	// Find the highest round number around
 	round := uint(0)