If the script layer is able to access the current node's config via
Supervisor::node(), it can handle populating Cluster::nodes. That code
is much more straightforward than an equivalent in-core implementation
(especially with the upcoming change to the cluster table's implementation).
This introduces base/frameworks/cluster/supervisor.zeek and
Cluster::Supervisor::__init_cluster_nodes() for that purpose.
The @load of the Supervisor API in cluster/main.zeek isn't technically
necessary since we already load it explicitly even in init-bare.zeek,
but being explicit seems better.
