Have swarm_server maintain N open peer connections

[madninja]

Have the swarm (through a session_agent) maintain a configurable set of connections to randomly selected peers.

• The configuration would ideally be a module name in the swam options with a simple default. So that applications can supply a more complex one if they have more context to be able to generate a diverse set of peer addresses from the peerbook.

• When agent detects a disconnected peer connection it should randomly select a new peer address and connect to it.

• Have the session_agent forget an existing connection on a regular schedule. It would then pick a new random address to connect to. The normal session timeout will end up closing the session.

• For the set of open connections also be able to supply the list of stream handlers to start for a newly opened connection.

• The simple policy uses a configuration list of seed_nodes passed in as part of Take an Options map in swarm:start  #42, and will select a number of (non-stale) nodes from the peerbook and at least one from the list of nodes specified in seed_nodes.

@Vagabond does this capture what we had in mind?

[Vagabond]

Yes, I think this sums it up nicely.