Update git submodules

* Update docs/submodules/releng from branch 'master'
  to 74f39df873503b71c46aca2acf53a65b5003477f
  - Run Vnf testing in parallel

    If it works, it will save an hour in all runs.

    Change-Id: I0f83d46c803538abdbf14d08e4188cd7f9737b85
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 6295d04..74f39df 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 6295d0499b748174341b7e99d8481d4f8da2b69f
+Subproject commit 74f39df873503b71c46aca2acf53a65b5003477f