Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Bugfix: Dovetail CI failed on fuel because of BRANCH: unbound variable

    JIRA: DOVETAIL-451

    1. Dovetail CI jobs failed on fuel becase lack of BRANCH.
       fetch_os_creds.sh: line 75: BRANCH: unbound variable
    2. That's mainly because of Dovetail uses sudo to run fetch_os_creds.sh.
    3. BRANCH is jenkins' env param and root's env lacks of this param.

    Change-Id: I3163d6e9f099e979bace00ce993b422ad60f6b8f
    Signed-off-by: xudan <xudan16@huawei.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 486d170..cebfb87 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 486d1700853be9e93181d3f0aa7a1b472a78e0e3
+Subproject commit cebfb874b5d9e759f9d97f8eee9d1d0a2dfab8ce