Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Workaround to fix Heat stack deletion bug in Shade"
  - Workaround to fix Heat stack deletion bug in Shade

    There is a bug in Shade, in the function "event_utils.poll_for_events".
    While Shade is waiting for the Heat stack to be deleted, retrieves
    periodically the status of this Heat stack. When the stack is deleted,
    the function "get_stack" [1] returns None; then L90 tries to access to
    a key of this None object.

    [1]https://github.com/openstack-infra/shade/blob/e5bcb705c5b32334cdc1dd9807126298c87b0622/shade/_heat/event_utils.py#L89-L90
    Shade function

    JIRA: YARDSTICK-1015

    Change-Id: I56ea853be41bfd7f63e094d7a3696d97ba078ba4
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 215740d..5ea8913 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 215740df982263cf3e2ae6581792856c365f0481
+Subproject commit 5ea891398c0f7404d568bbe813100b2488d677ed