Closes #10807 Adds support for `dockerfile` ONLY when `Dockerfile` can't be found. If we're building from a Dockerfile via stdin/URL then always download it a `Dockerfile` and ignore the -f flag. Signed-off-by: Doug Davis <dug@us.ibm.com> Upstream-commit: 15924f238503ffe44e5fcb99415ff753a36e5971 Component: engine