title: syslog-ng json parser does nothing
body: <p>My syslog-ng config is driving me insane. 
  I have an app, that puts out simple json log messages like:</p>
  
  <pre><code>{"level":"error","message":"connection ended without disconnect receipt","timestamp":"2018-10-12T17:49:08.650Z"}
  </code></pre>
  
  <p>All I want to do, is parse these 3 values and send them to a hosted Graylog cluster. Sending works, but the message gets inserted as</p>
  
  <pre><code>application name: {"level"
  message: "error","message":"connection ended without disconnect receipt","timestamp":"2018-10-12T17:49:08.650Z"}
  </code></pre>
  
  <p>it's almost like syslog-ng doesn't even interpret the file as json. I tried other variants, read the docs but I am at my wits end now...</p>
  
  <p>This is my config (on the application host; it should send the logs directly to the logging cluster)</p>
  
  <pre><code>@version: 3.5
  @include "scl.conf"
  @include "`scl-root`/system/tty10.conf"
  
  options { chain_hostnames(off); flush_lines(0); use_dns(no); use_fqdn(no);
         owner("root"); group("adm"); perm(0640); stats_freq(0);
         bad_hostname("^gconfd$");
  };
  
  source s_src { 
      file(
          "{{syslog_ng_src}}"
          flags(no-parse)
          );
  };
  
  template unitManagerTemplate {
      template("$(format-json --scope dot-nv-pairs) [sdid@123456 X-OVH-TOKEN=\"XXXXXXXXXXXXXXXXXXXXXXXXXX\"\n");
  };
  
  destination ovhPaaSLogs {
      tcp("gra2.logs.ovh.com"
          port(6514),
          template(unitManagerTemplate),
          ts_format("iso"),
          tls(peer-verify("require-trusted") ca_dir("/etc/ssl/certs/")),
          keep-alive(yes),
          so_keepalive(yes),
      );
  };
  
  parser p_json { 
      json-parser(prefix(".json.")); 
  };
  
  log {
      source(s_src);
      parser(p_json);
      destination(ovhPaaSLogs);
  };
  
  @include "/etc/syslog-ng/conf.d/"
  </code></pre>
  
  <p>I tried a different a template variant like this:</p>
  
  <pre><code>template("${.json.level} ${.json.message} ${.json.timestamp} [sdid@123456 X-OVH-TOKEN=\"XXXXXXXXXXXXXXXXXXXXXXXXXX\"\n");
  </code></pre>
  
  <p>Results where absolutely identical. I'd appreciate any help!</p>