Improve logging to aid in debugging transient issues

This works to clean up a lot of logging around vnodes, nodes and the network.

It includes:

* Prepending the host, port and partition in front of all log messages in skuld.vnode
* Providing a netty client exception handler
It's the only way to ensure that the `peer` attr is set on the channel before it waits to connect.

This allows for the `exceptionCaught` above to have access to the `peer` if the connection is refused (which actually happens a decent amount during tests).