Improve TuneD detection mechanism

[geragio]

This PR improves the detection mechanism for TuneD on the host system.
Previously, when TuneD was removed or absent, the system would generate an error when removing auto-cpufreq deamon or when starting the software in live mode:

* Enabling TuneD

Unit tuned.service does not exist, proceeding anyway.
Failed to enable unit: Unit file tuned.service does not exist.`

With this improvement, auto-cpufreq now gracefully handles the absence of TuneD without producing misleading errors.

[AdnanHodzic]

Great! Thank you for your contribution, you will be credited for your work as part of future release.