Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Update xtesting to 0.31

    It mainly fixes regex when INSTALLER_TYPE is unset [1]

    [1] https://gerrit.opnfv.org/gerrit/#/c/54089/

    Change-Id: I57430e87ec7b988337697417e319cf4f9b207e0d
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index be5a745..471128e 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit be5a74549a5c82e0588296b6638481e9555f686c
+Subproject commit 471128ebc1414eb6e97dcf444bf4f312ea24d6a5