feat(snmp_exporter): fix dry-runs on new machines

[pieterlexis-tomtom]

This does not fail a dry run on machines where snmp_exporter is not yet installed.

[gardar]

Is this really needed? ansible.builtin.systemd has full support for check_mode

[pieterlexis-tomtom]

Is this really needed? ansible.builtin.systemd has full support for check_mode

From what I have noticed: if you run this role in check mode on a blank slate, the unitfile is not put unto the system. When the service is started (or restarted) the dry-run will error out with Could not find the requested service snmp_exporter: host, stopping the dry-run. I can try to do some more experiments.