Update git submodules

* Update docs/submodules/releng from branch 'master'
  to 72f6fd79fac2f13c3cc08572f056b0f847916cdd
  - Force Xtesting docker build on lf-virtual1

    Xtesting pusblished on OPNFV Dockerhub organizarion.

    Change-Id: I0909065001f41afe804fdd553f5b39bb5af99510
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 94b5755..72f6fd7 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 94b57551c02f1cb1e4b7d0f0aef7ac67b4b27fe3
+Subproject commit 72f6fd79fac2f13c3cc08572f056b0f847916cdd