Filebeat ignores additional config files on syntax error

[breml]

If additional config files are defined with filebeat.config_dir and thous config files do have yaml syntax errors, these errors are silently ignored and filebeat is started normally. This is also true, if -configtest is used.

Version: current master

Steps to reproduce:

Have a filebeat.yml with filebeat.config_dir: /tmp/filebeat set.
Have an additional config file /tmp/filebeat/syntax_error.yml with content:

filebeat.prospectors:
- input_type: log
  paths:
    - /var/log/*.log
  exclude_files: [".gz\$"]

(the syntax error is in the last line, \$ is not a valid escape character.)