Update git submodules

* Update docs/submodules/releng from branch 'master'
  to a4c2cca3a5a0bc6deecbb87f42259d3199bbf30a
  - Run smoke in parallel back

    It's no simple to get the best threads (test cases and tempest) values
    and then guarantee Functest vs:
      - test flapping
      - backend limitations

    As opposed to the OpenStack gates, Jenkins runs all test cases in
    parallel which indirectly increases the number of threads.

    The SUT has been improved regarding the workers (divided by 2).
    The default value was too high due to the number of cpus.

    Change-Id: I09be861b9ec369f36447ac9e9c09d14f2b7da1a8
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 208bf65..a4c2cca 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 208bf65dafab76b8e6d74e72d60853efc1d230c4
+Subproject commit a4c2cca3a5a0bc6deecbb87f42259d3199bbf30a