According to documentation (https://docs.docker.com/engine/reference/builder/#dockerignore-file), absolute paths like `/foo/bar` should have the same effect as `foo/bar`. This is not the case today. This fix normalize paths when reading the .dockerignore file by removing leading slashes. Signed-off-by: Simon Ferquel <simon.ferquel@docker.com> Upstream-commit: 1cde87c43abd100f4233e965e040e30a6bd34112 Component: engine