Update git submodules

* Update docs/submodules/releng from branch 'master'
  - Merge "Functest: Introduce building image job for euphrates"
  - Functest: Introduce building image job for euphrates

    To build apline images for euphrates

    Change-Id: I63d77c99306aed263e220c2a0cd27ee2cca1ecb9
    Signed-off-by: Linda Wang <wangwulin@huawei.com>

diff --git a/docs/submodules/releng b/docs/submodules/releng
index d25197e..31056a7 160000 (submodule)
--- a/docs/submodules/releng
+++ b/docs/submodules/releng
@@ -1 +1 @@
-Subproject commit d25197e5d50d6a01e07dd52a9ca4d9c6ee33fd32
+Subproject commit 31056a7180802ecfcd3e8abb58e74911ef679642