Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Deprecate authentication variable OS_TENANT_NAME"
  - Deprecate authentication variable OS_TENANT_NAME

    OS_TENANT_NAME was deprecated as authentication variable in Keystone
    when moved from v2 to v3, in Icehouse (2014). Because this project doesn't
    support oldest versions, by default the only identification API version
    supported is v3.

    JIRA: YARDSTICK-902

    Change-Id: I273fb0151ba583f7c8a5a809e5e8864e92c27d31
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 3387e56..e670c9c 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 3387e5618de37c37714c86cec9058d737cb01a5c
+Subproject commit e670c9c6e165ee508bd509a3cd71f80c45d6d919