Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Remove KUBECONFIG from env_file"
  - Remove KUBECONFIG from env_file

    We have hardcoded /root/.kube/config as the default config file
    inside functest-kubernetes container:
    https://gerrit.opnfv.org/gerrit/#/c/53815/

    Change-Id: I135f2009c61bb0238fcc3c9eb6d131305603f495
    Signed-off-by: Linda Wang <wangwulin@huawei.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index 426b48d..cf9a902 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit 426b48dcc6d46da9ba988903387d1de498eecefd
+Subproject commit cf9a90212f9439e58d6cc38955cb1fe288f78ff8