Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "yardstick offline support"
  - yardstick offline support

    JIRA: YARDSTICK-597

    Currently yardstick can not run offline.
    In some case this will block the process, causing yardstick job failed
    The reason is yardstick will pull the latest code when run in CI.
    Actually we need not pull the latest code because the code in yardstick
    is already the latest code.
    So I remove them.
    Also I check the environment variable and yardstick-image when fetch
    openrc file and load images.

    Change-Id: I797da272932ab5292aa40585c82c119aa71b8849
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 3ab4604..ce91fca 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 3ab4604618224ea618083e1b5cd6fd8a1d81562a
+Subproject commit ce91fca5ade5ede330bf4c799dbffdf1b4762a9a