Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "add the ssh_key info if the key_file is exist"
  - add the ssh_key info if the key_file is exist

    Change-Id: I7a95933e254b35fc7b26d649226192b8e4c407bb
    Signed-off-by: dongwenjuan <dong.wenjuan@zte.com.cn>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index adfbaf2..21b4506 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit adfbaf2a3e8487e4c9152bf864a653a0425b8582
+Subproject commit 21b4506e546414bce99f491874e1eec15da3f4a0