Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Functest: fixes downloading images for danube branch

    The script for downloading images "download_images.sh" does not exist in
    stable/danube for functest.  Therefore we revert to old behavior for
    that branch.

    Change-Id: Id94f3db27fd5b71bb981007472b55fadae0e5394
    Signed-off-by: Tim Rozet <trozet@redhat.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index b78fb39..5907308 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit b78fb39202a79da6b88cede2da4dac696b31011f
+Subproject commit 5907308211e8d400f00f112ac47ad15057b70988