Update git submodules

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

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

    Intro is moved into a new file.

    Change-Id: Ic5c0108cf1cbb0fc69f7e2cc73cf2fb69e44baa1
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 319c283..87a9ed4 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 319c283565c4d7d38106487a12d3ce6a71cb4ba8
+Subproject commit 87a9ed4c08b2c7781f97bf03c08f2d4788f4653d