Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Set TEST_DB_URL in env"
  - Set TEST_DB_URL in env

    It follows the change "Move push_results_to_db to TestCase" [1] which
    stopped duplicating TEST_DB_URL in config and in env.

    [1] https://gerrit.opnfv.org/gerrit/#/c/49757/

    Change-Id: If860492c40b1d0ed4082a4dbe385686020697f37
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 9c0a34e..3fd9fd5 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 9c0a34eba94f87c6c5a02c52ccc521e9d5a6f4e8
+Subproject commit 3fd9fd53bbcd887a3189bc276408806f8ee8d64b