Ubuntu hosts should apt-get update before running unattended-upgrades

[SpComb]

The hosts/ubuntu should be running both apt-get update and unattended-upgrades, because unattended-upgrades will not update the APT indexes, and thus not upgrade any packages unless something else has run apt-get update beforehand.

By default with unattended-upgrades installed, the apt-periodic.timer will be updating the indexes twice a day, but the timer is randomized, so unattended-upgrades may or may not find updated packages to install.