Be able to name weave peers

[bboreham]

When studying logs and weave status output, it can get tiresome to keep mapping from the identity you know ("this is the node I run on EC2") to the hex peer-name used internally by Weave.

I propose that weave fetches the hostname of its container and displays it alongside the hex peer-name. It would also need to include this information in gossip messages so it is included in weave status on other peers.

The user would set the hostname by adding something like --hostname=ec2_node on the end of the weave launch command.

[bboreham]

Turns out this is not as simple as I thought, because --hostname will be passed to Weave as an argument, not to Docker.