Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Set STORAGE_PROTOCOL=ceph if Apex"
  - Set STORAGE_PROTOCOL=ceph if Apex

    It should fix most of errors raised by tempest_full [1].

    [1] https://artifacts.opnfv.org/logs/functest/lf-pod1/2018-10-20_12-23-41/tempest_full/tempest-report.html

    Change-Id: Ie93fe14d687a28185ac28b8c35636265a4fb4be2
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 2522d07..bd1831f 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 2522d0760f5f48803ddd31b3f8a9b98ef3c2d36c
+Subproject commit bd1831f3db50f284c6cd64577cbbebb70b2c0f4c