Since UnifiOS does not use the Java keystore (like a Unifi
Controller or Cloud Key Gen1 deploy), this also reworks
the settings validation and error messaging somewhat.
When running on a Unifi Cloud Key device, also deploy to
/etc/ssl/private/cloudkey.{crt,key} and reload nginx. This
makes the new cert available for the Cloud Key management
app running via nginx on port 443 (as well as the port 8443
Unifi Controller app the deploy hook already supported).
Fixes#3326
