When upgrading to percona-server-server-5.6, mysql_install_db still runs:
+ apt-get install -y --allow-unauthenticated percona-server-server-5.6=5.6.32-78.1-1.xenial~1
Reading package lists...
Building dependency tree...
Reading state information...
The following packages were automatically installed and are no longer required:
libperconaserverclient18 percona-server-common-5.5
Use 'sudo apt autoremove' to remove them.