Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Update python3 to python3.6

    It conforms with Alpine 3.8 (It updates the related tox entry).

    Change-Id: I7ba8e3cf5bae2f48ff5d802511a288446bca645a
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 0a0b2b3..b51417c 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 0a0b2b3e644e4ce353b37fa340954b78a590e20f
+Subproject commit b51417c9d2e7d34fec7d4bfa4fd723746e6b28e3