Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Bypass NoneType errors when creating router in rally

    It converts private subnet name to str as it's mandary till [1].
    It could be reverted as soon as [2] is merged in snaps.

    [1] https://gerrit.opnfv.org/gerrit/#/c/56091/
    [2] https://gerrit.opnfv.org/gerrit/#/c/56171/

    Change-Id: Ia728415207f8ecb5b5ac55982f82337c45671c4c
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index c61ea93..f0870e3 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit c61ea93a8414f824e7c26cf78e5c52ee8220963c
+Subproject commit f0870e3735324941f5bd77243f36f9214cd531ac