Update git submodules

* Update docs/submodules/releng from branch 'master'
  to 28359b18dde956af4ff57b9b0e469e484ca280f7
  - Create Xtesting stable/jerma branch

    OpenStack just published stable/train [1]

    [1] https://github.com/openstack/requirements/tree/stable/train

    Change-Id: I5807dbc033f902e7255478d47138b8cfeed54d0f
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 6f177a7..28359b1 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 6f177a756e0b034f640bdc12deecb1fb479c11dd
+Subproject commit 28359b18dde956af4ff57b9b0e469e484ca280f7