Make deprecation of clustered option work and document HQ221038

This is the promised update to Pull#997 (removed duplicate prefix).

Currently HornetQ always prints the deprecation message, with this fix it will only be printed when the option is actually present. This fix also adds the log message ID to two places in the documentation to make it easier to find.

Further improvements would be to remove the default value for the element in the configuration schema and possibly make the deprecation message a warning.