Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Allow overriding DOCKER_TAG in functest-alpine.sh"
  - Allow overriding DOCKER_TAG in functest-alpine.sh

    It's mainly required by functest-apex-baremetal-daily-master which
    runs vs OpenStack master and OpenStack Rocky.

    Change-Id: I5e32f5b507fbe79a02bf5c61e67aa7f8c24f7789
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 2e54805..9b16462 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 2e54805dc614814cd2b7c09621549bab1538bb01
+Subproject commit 9b164628deaf8bc495d4eabdb6458add7175cd32