Same issue and same apparmor messages in syslog when upgrading from 14.04.4 to 16.04.1. Thomas' workaround of killing "/var/lib/dpkg/info/cups-daemon.postinst configure 1.7.2-0ubuntu1.7" allowed the upgrade to continue, but it'd be nice not to see this kind of issue on an LTS > LTS upgrade.
Same issue and same apparmor messages in syslog when upgrading from 14.04.4 to 16.04.1. Thomas' workaround of killing "/var/lib/ dpkg/info/ cups-daemon. postinst configure 1.7.2-0ubuntu1.7" allowed the upgrade to continue, but it'd be nice not to see this kind of issue on an LTS > LTS upgrade.