Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Merge "Stop using master for pip"
  - Stop using master for pip

    Rally cannot work via latest pip:
      [r.name.lower() for r in pip.req.parse_requirements(
      rally AttributeError: 'module' object has no attribute 'req'

    Badly it forbids building containers from a gerrit change.

    Change-Id: Ie60344b2a7793729823643ba2c1d3c30500d56c4
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 6df9538..d337aaa 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 6df95384eb26cdca150f7010bcead9e93d8aac4a
+Subproject commit d337aaa51d74314544c36ca30b6951cec1156d5d