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