replace logging component of file scanning

[mmguero]

The code that handles the logging in file-monitor, logging the results of the file scanners like capa, clamav, yara, etc., is just of hacky, in that it writes to sort of a fake Zeek signatures.log file that gets handled with the rest of the zeek logs.

I want to change that logging code to skip that intermediate step and simply send straight to logstash (or, if that's not possible, our filebeat TCP listener) instead. This will be something that will make it easier to handle more varied output from Strelka (see #485),