gitlab-ci for test jobs

[Ross Vandegrift <ross@kallisti.us>]

Hi everyone,

First complete pass at a framework for running tests is here:
https://salsa.debian.org/cloud-team/debian-cloud-images/merge_requests/36
It's working, you can see the last run at:
https://salsa.debian.org/rvandegrift-guest/debian-cloud-images/pipelines/21750

This is the simplest config I could find that has a separate test job for each
build job.  It's complex and verbose.  Makes it hard to know that all of the
cases are covered.

One alternative: extend the .build job scipt to run tests after FAI.  The
benefit: a new build job automatically gets tests run without manually creating
a new job.  The downside: if a job fails, you have to dig through logs to
determine if the build failed or if the tests failed.

If we go with separate jobs, we could add a CI-linting stage before the build.
This could check the pipline to ensure e.g., every build has a test, only
official builds get run on casulana, etc.

Any thoughts on the tradeoff, or maybe a better idea?

Ross