Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Pull the latest parent when building containers"
  - Pull the latest parent when building containers

    Change-Id: I534c14f4415c16661fb95966077621497c6f9cdc
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 6bfe687..6977c4f 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 6bfe687fbd6dcf57a9096a4ea356ef98561d3d18
+Subproject commit 6977c4f63ee17be70d90a5b800e3d9cde0ea33c2