Change the logging infrastructure to handle when the node name isn't
available in `elasticsearch.yml`. In that case the node name is not
available until long after logging is configured. The biggest change is
that the node name logging no longer fixed at pattern build time.
Instead it is read from a `SetOnce` on every print. If it is unset it is
printed as `unknown` so we have something that fits in the pattern.
On normal startup we don't log anything until the node name is available
so we never see the `unknown`s.
Nik Everett