Update git submodules

* Update docs/submodules/yardstick from branch 'stable/euphrates'
  - Merge "Doc amendment: env prepare command" into stable/euphrates
  - Doc amendment: env prepare command

    JIRA: YARDSTICK-637

    Change-Id: I7e5e1afb7b5a7e97aa070c03cded3be285d97cc2
    Signed-off-by: JingLu5 <lvjing5@huawei.com>
    (cherry picked from commit d91ddc83daa7ac112c764e74621b48455d038e7f)

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 4608b2d..9c0a94c 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 4608b2d7a467344cde6208eaa5d0db58d7d7d42f
+Subproject commit 9c0a94c9dc4966b6f0443c119d7ae8a0602bd39d