Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Generate xtesting.yaml from playbook

    It takes into account the update of Alpine (3.9).

    Change-Id: Ied99214e23717f8848fbc2072581ab309772fb1b
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 07be796..7c5ec61 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 07be796a1d5ebf3864679b49d5219f946c65e10a
+Subproject commit 7c5ec611f2190ab402449bc2a2049d6bde4263c8