Update git submodules

* Update docs/submodules/releng from branch 'master'
  - opnfv-docker.sh: Fix unbound ARCH_TAG

    Jenkins does not set ARCH_TAG to an empty string; instead it does
    not set that variable at all when the input is empty.
    Fix this by providing a default empty string in the script.

    Change-Id: Iec4c38068b1ab3e8dd124f49b36759eedb084f4a
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 6b30c00..23829e1 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 6b30c00a481d452d1b9ee4468054ce59e631f19a
+Subproject commit 23829e1180fb8106a4a13fbbb6decf9217f291e4