Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Move tests: unit/cmd/"
  - Move tests: unit/cmd/

    * Fix pylint errors
    * Add TODOs

    Some errors are ignored locally, as they were a symptom of other problems.
    These issues have been flagged with a TODO, and should be fixed later.

    Change-Id: I505d72e1c646fea1976a0bf854369c6b6308bbb1
    Jira: YARDSTICK-837
    Signed-off-by: Emma Foley <emma.l.foley@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 69d5e6b..39c6a19 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 69d5e6b288d16b5f9cab57859670d651eccd5e26
+Subproject commit 39c6a194fe2c3f97b4689d6eb5ef8feac11da685