connect() unconditionally stored server_name as local_node, and
update() filtered instances whose location did not match. On a
standalone LXD host, instance.location is empty, so every container
was dropped and the user saw no LXD stats at all.
Gate the filter on environment.server_clustered — only apply the
cluster-member filter when the daemon reports itself as clustered.
Also promote the connect() failure log from debug to error so that
future connectivity issues are visible in the default log.
