Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Bugfix:add storperf flavor for TC074"
  - Bugfix:add storperf flavor for TC074

    JIRA: YARDSTICK-604

    the storperf container now uses a flavor called "storperf", if this flavor is
    absent, stack creating process will fail. also the openstack variables that
    passed to the storperf container also needs a update

    Change-Id: Iab4be6491cc9b24526948e5571f0476ec885a93d
    Signed-off-by: JingLu5 <lvjing5@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 4c1b439..355f683 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 4c1b439ccd286dc8c8a84cd8eed57d1b230c6177
+Subproject commit 355f6833772f06b7935c58d2b15f9a1f3409c28b