main: unif/refactor std{out,err} test handling#416

mvo5 wants to merge 3 commits intoosbuild:mainosbuild/image-builder-cli:mainfrom

mvo5:add-boostrap-container-always-plus-cmdline-test-cleanupmvo5/image-builder-cli:add-boostrap-container-always-plus-cmdline-test-cleanupCopy head branch name to clipboard