Update git submodules

* Update docs/submodules/releng from branch 'master'
  to d573696d9d5e3b1c617cb38377cb8975c113d683
  - Updates ca-certificates in all tox jobs

    https://build.opnfv.org/ci/job/functest-kubernetes-latest-tox/100/console

    Change-Id: I0f9031026bb332f0e03032270d2b8fe02f08e73b
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 21fad69..d573696 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 21fad69b5a67fced68aa9c7d51923df74f28ee0b
+Subproject commit d573696d9d5e3b1c617cb38377cb8975c113d683