Merge dont-restart-services-unnecessarily [f=1463697] [r=bjornt,adam-collard,landscape-builder] [a=Free Ekanayaka]
This branch makes the LSCtl callback a bit smarter and avoid restarting services in a few situations that don't require a restart. For instance:
- If the SSL certificate change (since we don't load it in memory)
- If the postgresql relation data changed in a way that doesn't affect connection details (for example a new landscape-server unit was added and it's popping up in the allowed_units key).
There is also a small cleanup of repeated logic for finding a certain key in the required_data list of a ServiceManager.