Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Switch to the readthedocs theme for api docs

    It also adds a requirement file for external doc tools wich couldn't
    handle upper constraints.

    Change-Id: Idf8f43e5e1a845055ce248f1dc8b8d676a3ac37b
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 8f23ca1..7b8e07e 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 8f23ca12081c369423eab9456f8629b9c9680602
+Subproject commit 7b8e07e9100974a506c7dd31c8bf190ecf69840c