Avoids a stale cache condition during CI-build

[danv61]

CI-build failed with the following:

E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/e/expat/libexpat1_2.4.7-1ubuntu0.7_amd64.deb  404  Not Found 
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
ERROR: process "/bin/sh -c apt -y update && apt install -y software-properties-common" did not complete successfully: exit code: 100

Diagnostics: run apt update in one layer, docker caches the layer, ubuntu rotates security updates
run apt install using the cached, stale data

Fix: combine update and install into a single run

Fixes #1641