Comment 3 for bug 1574782

Files affected:
* d/additions/mysqld-systemd-start
 Sanity check fails is /var/lib/mysql and /var/lib/mysql/mysql do not exist
 Maybe not needed since the server error by itself should be sufficient if the configured datadir is missing

* d/additions/apparmor-profile
 Read/write permissions to datadir. Can probably expect users to change the profile if they want a custom datadir, but document/warn about it somewhere?

* d/postinst:
 Creates datadir, sets ownership and runs initialize if empty. Will need to check config for correct one to prevent it from trying to create and populate /var/lib/mysql even if user wants it somewhere else (upstream scripts have some code to do this).

* d/postrm:
 Data removal on purge. Not all that important

5.7 also creates /var/lib/mysql-files and /var/lib/mysql-keyring, but they aren't as important for installation