One openQA template to rule them all, and no shell scripts

With !45 (merged) we now have 3 Gitlab CI scripts that start openQA tests:

• one in templates/gnomeos-test-sysext.yml in this repo
• one in openqa-tests.git test-s3-image job
• one in gnome-build-meta.git test-s3-image job (which is slightly different as it clones openqa-tests.git into gnome-build-meta.git)

A related issue is that to use templates/gnomeos-test-sysext.yml, one has to duplicate six scripts into the component repo:

• openqa/utils/fetch_test_media.sh -- this is a tiny wrapper around curl
• openqa/utils/expand_disk.sh -- this is a small wrapper around dd
• openqa/utils/setup_worker.sh -- this creates the /etc/openqa/workers.ini file with a unique WORKER_CLASS, so we can have transient workers
• openqa/utils/start_all_jobs.sh -- this uses openqa-cli to submit a job, and parses the JSON response to a temporary file, so the main script can poll the status of each job
• openqa/utils/wait_for_job.sh -- this uses openqa-cli to poll the status of each job in a loop, exiting with success/failure appropriately
• openqa/utils/openqa_junit_report.py -- use the openQA REST API to get the results for each job and generates a JUnit XML test report, to integrate with Gitlab's test results view

Ideas for removing these:

• openqa/utils/fetch_test_media.sh -- just use curl directly in the CI template
• openqa/utils/expand_disk.sh -- use dd directly
• openqa/utils/setup_worker.sh -- just write /etc/openqa/workers.ini directly in the CI template. (Or come up with a better solution for this upstream -- see https://github.com/os-autoinst/linux-qa/issues/2)
• openqa/utils/start_all_jobs.sh -- extend the openqa-cli tool to write the job IDs in the format we want
• openqa/utils/wait_for_job.sh -- add a subcommand of openqa-cli to do what we need
• openqa/utils/openqa_junit_report.py -- add the script upstream, or add a subcommand of openqa-cli to do what we need

One issue of moving functionality back into the .gitlab-ci.yml is that it can be harder to test in isolation. https://github.com/firecow/gitlab-ci-local might help there.