Update git submodules

* Update docs/submodules/functest from branch 'stable/euphrates'
  - Merge "Force python2.7 when creating venv for refstack" into stable/euphrates
  - Force python2.7 when creating venv for refstack

    It applies part of "Fix rally db issue" [1] which is not
    cherry-picked because it mainly focused on rally updates.

    [1] https://gerrit.opnfv.org/gerrit/#/c/47555/

    Change-Id: Ic6850e54860fe2b54a2199e1c3ed89d822ae6284
    Signed-off-by: Linda Wang <wangwulin@huawei.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 4cce1dd..821a07c 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 4cce1dde601ce15dad888644a96ff343064dc29d
+Subproject commit 821a07c25a55ee60993c2864e0930338d67f4d21