Add test for ignoring invalid dockerfile instructions

Signed-off-by: Tibor Vass <teabee89@gmail.com>
ignore invalid Dockerfile instructions and do not consider "docker-version" a Dockerfile instruction

Signed-off-by: Tibor Vass <teabee89@gmail.com>
Merge pull request #8434 from tiborvass/ignore_invalid_Dockerfile_instructions

Ignore unknown dockerfile instructions