Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Add "stdin" and "tty" parameters to Kubernetes container

    JIRA: YARDSTICK-1330

    Change-Id: I05303a1d0783421472883806f97441dd63f7f740
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>
  - Accept strings and lists as container "args" and "commands"

    Accept strings and list of strings as "args" and "commands"
    in a Kubernetes container.

    JIRA: YARDSTICK-1329

    Change-Id: I56470741072fb7f9a62d695c51fcb0cc3f3ff1b9
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 4e058b7..5b37f2e 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 4e058b76a3f9edd26b60f2eeaf4a4ff95e7aa0a6
+Subproject commit 5b37f2eb188c390ce6942940e0ad9f33900dafd5