Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Use cirros-0.4.0 rather than cirros-0.3.5 for Functest Fraser.

    Change-Id: If3cd0fe52d946979de259951c7c8433b6e1e42f0
    Signed-off-by: xudan <xudan16@huawei.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index cf1ba3b..751447b 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit cf1ba3b2c19202a17fdd12a9ada8ca3a1f3f627a
+Subproject commit 751447bbe93e412c993efb50c7769413724e16f0