Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Remove yamllint from upper-constraints.txt

    OpenStack doesn't list test requirements in upper constraints [1].

    [́1] https://github.com/openstack/requirements/blob/stable/pike/upper-constraints.txt

    Change-Id: I7472158d385beb311c159563bc3bb973c4a2d4c7
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index f424ff1..8f23ca1 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit f424ff12f6bdb7ef87f3982b7eb058716050457b
+Subproject commit 8f23ca12081c369423eab9456f8629b9c9680602