[18.09 backport] Allow overriding repository and branch in validate scripts, and no need to git fetch in CI Upstream-commit: 02c953cf36fa4f017be402451106d9c273023b4f Component: engine
[18.09 backport] Allow overriding repository and branch in validate scripts, and no need to git fetch in CI Upstream-commit: 02c953cf36fa4f017be402451106d9c273023b4f Component: engine