* swarm/network: WIP consider all nodes for healthy iteration

* swarm/network/simulation: extend TestWaitTillHealthy to really check kads are healthy

* cmd/swarm/swarm-snapshot: fixed bugs in snapshot creation binary

* swarm/network/simulation: addressed PR comments

* swarm/network/simulation: defer sim.Clsoe()

* swarm/network/simulation: fixed wrong sim.Close()

* swarm/network/simulation: addressed PR comments

* cmd/swarm/swarm-snapshot: reducing default to 8 nodes, more to 4

* cmd/swarm/swarm-snapshot: extended timeout to 3 mins, or 256 nodes snapshot times out

* swarm/network/simulation: More PR comments