When a node does not have gossip STATUS application_state, we currently
use an empty string to present such state in get_gossip_status.
It is better to use an explicit "UNKNOWN" to present it. It makes the
log easier to understand when the status is unknown.
Before:
'gossip - InetAddress n2 is now UP, status ='
After:
'gossip - InetAddress n2 is now UP, status = UNKNOWN'
This patch is safe because the STATUS_UNKNOWN is never sent over the
cluster. So the presentation is only internal to the node.
Fixes#5520
343986a70b