Eventscript functions: optimise ctdb_check_tcp_ports() and add debug.

Eventscript functions: optimise ctdb_check_tcp_ports() and add debug.

ctdb_check_tcp_ports() runs "netstat -a -t -n" in a loop for each
port.  There are 2 problems with this:

* Netstat is run on each loop iteration when it need only be run once.

* The -a option is used to list all connections but the function only
  cares about the listening ports.  There may be many thousands of
  non-listening ports to grep through.

This changes ctdb_check_tcp_ports() to run netstat with the -l option
instead of the -a option.  It also only runs netstat once before the
main loop.

When a port is found to not be listening the output of the netstat
command is now dumped to help with debugging.

Signed-off-by: Martin Schwenke <martin@meltin.net>