Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Bug fix ansible scripts"
  - Bug fix ansible scripts

    For 'qemu-img version 2.10.1' unit 'MB' is not acceptable
    Changing to 'M'

    JIRA: YARDSTICK-1019

    Change-Id: Ic9153e9e9c85d949d15b1d15cc8cddfad986b4a3
    Signed-off-by: John O Loughlin <john.oloughlin@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 7a78031..b770a28 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 7a78031d2a8daabd880e33b26bc7414780f36a14
+Subproject commit b770a2891b6bd9cde38f4062abf700280c5cc4f0