Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Fix Functest User Guide

    It allows building this documentation via tox.
    rst files are now checked via doc8.

    Intro is moved into a new file.

    Change-Id: If1dbe2cbde2f39ca4948ada2b2743594bc387dbc
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 87a9ed4..3756ff6 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 87a9ed4c08b2c7781f97bf03c08f2d4788f4653d
+Subproject commit 3756ff6fbd17269fd9d2a585d3d0ef4bea6f6f9e