allow wildcard filenames

this will allow to specify wildcard filenames, but as rsyslog cannot handle them as they are, we're going to expand the path to the actually matching files and making an entry for each of them.

given `/var/log/a.log` and `/var/log/b.log`

when our node is configured like this:

    "watch_files": {
      "/var/log/*.log": "foo"
    }

this will result in an entry for `a.log` and `b.log` both tagged as "foo"