Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Bugfix: Error validating value 'cirros-0.3.5'"
  - Bugfix: Error validating value 'cirros-0.3.5'

    JIRA: YARDSTICK-607

    some scenarios come with a Cirros-0.3.5 image, Yardstick's load_images.sh will
    load a second cirros-0.3.5 image, causing the following error:
    2017-03-27 07:42:58,317 yardstick.orchestrator.heat heat.py:449 INFO Creating stack 'demo-2ada98f3'
    error: failed to deploy stack: 'ERROR: Property error: : resources.ares.demo-2ada98f3.properties.image: : Error validating value 'cirros-0.3.5': No images unique match found for
    {'name': u'cirros-0.3.5'}

    This patch fixs this error by skipping load cirros image if there already exist
    one in the glance.

    Change-Id: I4d43d82d331f6575efd4560be9b6be175e03cd1b
    Signed-off-by: JingLu5 <lvjing5@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 355f683..2eca9b5 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 355f6833772f06b7935c58d2b15f9a1f3409c28b
+Subproject commit 2eca9b5a2de0e2c02e7ba3991944f01761679d3f