Sporadic SSSD dependency error during build

[mikkonie]

Adding as a separate ticket from #16 for easier follow-up. I've observed this sporadically without making any changes in SSSD dependencies:

4.142 E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/c/cups/libcups2_2.3.1-9ubuntu1.8_amd64.deb  404  Not Found [IP: 185.125.190.83 80]
4.142 E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
4.142 Fetched 14.5 MB in 2s (8330 kB/s)
------
Dockerfile:125
--------------------
 123 |     
 124 |     ARG DEBIAN_FRONTEND=noninteractive
 125 | >>> RUN apt-get install -y sssd sssd-ldap sssd-tools strace
 126 |     
--------------------
ERROR: failed to solve: process "/bin/sh -c apt-get install -y sssd sssd-ldap sssd-tools strace" did not complete successfully: exit code: 100

This seems to happen occasionally. Possibility to switch to a more stable package source?

[mikkonie]

Fixed, just had to add apt-get update in the sssd stage.