sysutils/logstash6: Many improvements

• all config files are now in ETCDIR
• rc script is updated to use logsearch.yml to locate logging config (logstash.conf) This will not break existing setups that used the ETCDIR/logstash.conf file, as that is now part of the default logstash.yml file
• added configtest to rc script
• sample logstash.conf file no longer includes invalid syntax
• pkg-message had historical messages removed