Cluster: process MEET packets as PING packets.

Somewhat a previous commit broken this so CLUSTER MEET was no longer
working.
Cluster: fix CLUSTER MEET ip address validation.

This was broken by the IPv6 support patches.
Print error message when can't bind * on any address.
Opening TCP listening ports refactored into a function.
Use listenToPort() in cluster.c as well.
Cluster: set event handler in cluster bus listening socket.

The commit using listenToPort() introduced this bug by no longer
creating the event handler to handle incoming messages from the cluster
bus.