Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "bugfix: hosts should be clean if update_hosts twice"
  - bugfix: hosts should be clean if update_hosts twice

    JIRA: YARDSTICK-774

    Change-Id: Id610d43d236ab3a7d1aa4b8cfd230a40958fac38
    Signed-off-by: rexlee8776 <limingjiang@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index a862619..80c1d81 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit a8626195f5e8530f989693a7d8dc73f97ebe115b
+Subproject commit 80c1d81ead5a5416e7e40f49ffc80a525e5737e0