Update test suite images

Background

With buildstream-docker-images!49 (merged) we have finally started the process of restructuring our image repository. This means that our test runner is running with images that we would like to deprecate!

Task description

The test suite images for our CI should be updated:

• buildstream-fedora -> testsuite-fedora:27
• buildstream-debian -> testsuite-debian:9

Acceptance Criteria

All our test suite images should use the new images, so that we can deprecate the old images.

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