Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Apex: fix overcloudrc unsetting OS_VERSION

    Sourcing overcloudrc is unsetting OS_VERSION causing failures in csit
    job:
    https://build.opnfv.org/ci/job/cperf-apex-csit-master/1/console

    Change-Id: Ife3b4795832ecdad75bcb41f0721ef8391aafcac
    Signed-off-by: Tim Rozet <trozet@redhat.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 66baed3..b237878 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 66baed3706f01f673f6a6cb9ce0a2d3dba8ab492
+Subproject commit b23787845e719f39d4a48f0581be2019764f73ed