Update git submodules

* Update docs/submodules/functest from branch 'master'
  - Get properly env vars or their default values

    It defines env.get() as an unique way to get Functest env vars or
    their default values. It can be considered as a wrapper above os.environ.

    It enforces backward compatibility via CONST which mustn't be used
    for that purpose. It should be noted that it also stops using CONST
    for getting OpenStack env vars.

    Change-Id: I333dc1afbc0123166a7eaff8b551370098efa341
    Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/docs/submodules/functest b/docs/submodules/functest
index 98e2806..d589e4e 160000 (submodule)
--- a/docs/submodules/functest
+++ b/docs/submodules/functest
@@ -1 +1 @@
-Subproject commit 98e2806cb674d206dea65647c0644dc5b2871b4b
+Subproject commit d589e4e5345ed82c68d9a011ac89f8cdbefe2ca3