Cover case when config file is in different location than binary

[r-savcenko]

Check if result of exec contains "error". This covers cases when filebeat config is not in the same directory and result of the exec is not empty, but rather Loading config file error: Failed to read /usr/bin/filebeat.yml: open /usr/bin/filebeat.yml: no such file or directory. Exiting. which further cannot be parsed as a valid version.

The case:

# systemctl status filebeat.service
● filebeat.service - filebeat
   Loaded: loaded (/usr/lib/systemd/system/filebeat.service; enabled; vendor preset: disabled)
   Active: active (running) since Wed 2023-04-05 13:18:33 CEST; 9 months 20 days ago
     Docs: https://www.elastic.co/guide/en/beats/filebeat/current/index.html
 Main PID: 751 (filebeat)
   CGroup: /system.slice/filebeat.service
           └─751 /usr/bin/filebeat -c /etc/filebeat/filebeat.yml

The result without fix:

# facter -p filebeat_version --trace
2024-01-25 06:03:37.224036 ERROR puppetlabs.facter - error while resolving custom fact "filebeat_version": undefined method `[]' for nil:NilClass
backtrace:
/opt/puppetlabs/puppet/cache/lib/facter/filebeat_version.rb:34:in `block (2 levels) in <top (required)>'

The result with fix:

# facter -p filebeat_version --trace
1.3.1