Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "[Functest] Adapt set-functest-env to download OS images"
  - [Functest] Adapt set-functest-env to download OS images

    When [1] is ready and merged, we don't need to download the
    OS images that are not needed for the deployed scenario.
    The same filter applies to armband jobs.

    [1] https://gerrit.opnfv.org/gerrit/#/c/37373/

    Change-Id: I5813c738a8d9fa1262299cc50993557757f6d7e8
    Signed-off-by: jose.lausuch <jose.lausuch@ericsson.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 3983bb3..c6cb6fa 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 3983bb3199ed4d8b9cb3cfc51ac3dd064199b2f3
+Subproject commit c6cb6fae1560345d44a457e990f009b350835a1e