Update git submodules

* Update docs/submodules/releng from branch 'master'
  to c6e40603d8e326753bb47ed04df496629fd88b56
  - Leverage on S3 support in Xtesting

    It avoids using gsutil in Jenkins (extra logics).

    Change-Id: I0494875883436da5846d99e1088812793c46af72
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 5c75d37..c6e4060 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 5c75d372ebd4d090748c1f7cb8b1847652c6be6c
+Subproject commit c6e40603d8e326753bb47ed04df496629fd88b56