Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Temporarily download cirros from artifacts

    The domain download.cirros-cloud.net expired 2017-08-27, meaning
    cirros image downloads fail, so change the download url to artifacts
    temporarily.

    Change-Id: I26e0723b5df1300c3869cc2f4cad138794c17e4b
    Signed-off-by: Linda Wang <wangwulin@huawei.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 78be021..c5152e5 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 78be021d910088aeced1b62c9d00dffa33f74ca3
+Subproject commit c5152e5ca372ba661f6669c67b51bbe0bb9d9e26