Test suite improvements from buster sprint 1

This includes the fabled --fuzzy-image-matching option for the automated test suite, among a few other minor fixes.

Please review’n’merge into devel.

Feature Branch: test/improvements-from-buster-sprint

Related issues

• Blocks #13240 (closed)
• Blocked by #15007 (closed)
• Blocked by #14929 (closed)
• Blocks #14874 (closed)

Original created by @anonym on 14817 (Redmine)