Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Improve VMs spawning for OpenStack"
  - Improve VMs spawning for OpenStack

    In some, like 5% or so, VMs become not responsible. Added a validation to make sure VMs
    are reachable over SSH. In case of issue - restarting VM.

    JIRA: YARDSTICK-1141

    Change-Id: I110fe35b4b7bdbc4ba962d3814ce0f8cd40e5400
    Signed-off-by: Stepan Andrushko <stepanx.andrushko@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index d636d81..a3d1c85 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit d636d815e7c51594340e19478b4470f32a3ca25c
+Subproject commit a3d1c85482159201492284d1c893cebda91003b3