Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Bug fix for Ansible destroy VM script"
  - Bug fix for Ansible destroy VM script

    Modified the destroy script to ignore errors as 2 possible
    problems can cause a play to fail.
    1. A VM can be running but undefined.
    2. A VM can be destroyed but still running.

    JIRA: YARDSTICK-1006

    Change-Id: Ib66f48401bfefb598f553cfef31bfa2682f5a584
    Signed-off-by: John O Loughlin <john.oloughlin@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 4946bfb..a0e7bc3 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 4946bfbee16b9738a996d7ec6750caa9c064d156
+Subproject commit a0e7bc354558278d3f566e8abe9886e18050e887