Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Merge "Switch to stestr"
  - Switch to stestr

    It also updates rally and installs rally-openstack.
    It completes the update to OpenStack Queens.

    Change-Id: Iabf436ac6e7facfa21a3d7c8a3dfaffa9142da98
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 1e1b6e4..36acb25 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 1e1b6e46a650c09602c3787391294789e9cc2ebc
+Subproject commit 36acb258118f65eb99e99feaaa9a2c5796cfa1a3