The Debian package postinstall does a poor job of checking for an apparmor installation, which ultimately can cause the install to fail.  The only check the script does is 

if [ -f /etc/apparmor.d/usr.sbin.mysqld ]

If this succeeds, it assumes apparmor is installed.  This is not the case, and when it tries to run 

/etc/init.d/apparmor restart

the installer will fail (assuming it doesn't exist).  It should be trivial to mod the installer to check for the existence of /etc/init.d/apparmor before actually trying to run it.