Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Run vnfs sequentially in gates

    We are facing with issues due to shared bandwidth and the number of
    vms.

    Change-Id: I84dc188db08455f01ac6a9046cd8fd95645853cb
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 96eb8c1..a3bd7f5 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 96eb8c1a25207f55634f4cf84edaaad6143342e6
+Subproject commit a3bd7f544347cdd2c4811768bb7232a4b299bbce