New feature: Simplify Watchdog related configuration parameters.

New feature: Simplify Watchdog related configuration parameters.

This commit simplifies watchdog related configuration parameters
by using a common config file for each pgpool node and a pgpool_node_id file.

Previously we need to configure the following parameters on each pgpool node,
because of the difference between local and remote pgpool nodes settings.
- wd_hostname
- wd_port
- wd_heartbeat_port
- heartbeat_device
- heartbeat_destination0
- heartbeat_destination_port0
- heartbeat_destination1
- heartbeat_destination_port1
- other_pgpool_hostname0
- other_pgpool_port0
- other_wd_port0
- other_pgpool_hostname1
- other_pgpool_port1
- other_wd_port1

This commit simplifies watchdog related configuration by using a common config file
for each pgpool node and a pgpool_node_id file, and users just copy the configuration file
to each pgpool node without editing.

The parameters above are changed to (for 3 pgpool nodes):
(For example)
==============================
 hostname0 = 'server1'
 wd_port0 = 9000
 pgpool_port0 = 9999

 hostname1 = 'server2'
 wd_port1 = 9000
 pgpool_port1 = 9999

 hostname2 = 'server3'
 wd_port2 = 9000
 pgpool_port2 = 9999

 heartbeat_hostname0 = 'server1'
 heartbeat_port0 = 9694
 heartbeat_device0 = ''

 heartbeat_hostname1 = 'server2'
 heartbeat_port1 = 9694
 heartbeat_device1 = ''

 heartbeat_hostname2 = 'server3'
 heartbeat_port2 = 9694
 heartbeat_device2 = ''
==============================

You can specify multiple configurations in "heartbeat_hostname" and "heartbeat_device" by separating
them using semicolon (;).

And user needs to specify local pgpool node id in a pgpool_node_id file on each pgpool node.
pgpool_node_id file should be created in the direcroty of pgpool.conf.

In addition, this commit increases "WD_MESSAGE_DATA_VERSION_MINOR" to "2".