Update git submodules

* Update docs/submodules/releng from branch 'master'
  to ccd6e3781dee56ab6c58a19a1617f65564acfa8a
  - Clean all airship artifacts too

    Change-Id: I503084b5136b7cc061351e9c3dd2812000925754
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 0e8d4e0..ccd6e37 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 0e8d4e0c868951f1ae3dce7fb3b78cd5a57785a8
+Subproject commit ccd6e3781dee56ab6c58a19a1617f65564acfa8a