Better indication of refusing to start because of ProtectHome

I just spent unreasonable amount of time until I learnt about existence of the `ProtectHome` setting. My use case is I needed to change the directory to home because I don't have space anywhere else on my dev environment (which I think could be common)

I believe when mariadb refuses to start because ProtectHome=true it is not logged/displayed, not obvious to someone who doesn't know about this setting.

Please ignore/close the issue if this is not true and I just didn't see it