Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Allow building docker image from specified path

    Change-Id: Iab40fc2c719050d36a614fe529ca22634b59b7bc
    Signed-off-by: Yujun Zhang <zhangyujun@gmail.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 6b5e80b..c019ec5 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 6b5e80b0de5b166d7a790b219424c78b79221557
+Subproject commit c019ec5a0f10b81673e0cf29da3df4e8404bf21e