Domain directory-grouping should group directories by server name when set to by-server

Currently if the /host=master/directory-grouping=by-server is set the same directory will be used for all servers if the jboss.server.xxx.dir is overridden. For example of the jboss.server.log.dir is overridden all servers in the group write to the same server.log file. They should be in $jboss.server.log.dir/server-name/ directory.