MINOR: server: cli: Add server FQDNs to server-state file and stats socket.

MINOR: server: cli: Add server FQDNs to server-state file and stats socket.

This patch adds a new stats socket command to modify server
FQDNs at run time.
Its syntax:
  set server <backend>/<server> fqdn <FQDN>
This patch also adds FQDNs to server state file at the end
of each line for backward compatibility ("-" if not present).