Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Integrate vsperf in Tgen mode

    Problem:
    Running Vsperf in Tgen mode is supported but the integration is not complete at the code level
    i.e. not ready-to-use, and dpdk loopback is not supported inside the VM.

    Solution:
    (1) Completely automates VM image generation and supports 1G huge pages.
    (2) Adds a new test scenario VsperfDPDK for testpmd based loopback inside the VM.

    Update 1-2: Fixed "line too long" issues not reported by local run_tests.sh (why?)
    Update 3: Per comment change to use SSH.from_node() and add unit test cases
    Update 4: Add more unit test cases for coverage and ready the code for merge

    JIRA: YARDSTICK-661

    Change-Id: Iea3014d4c83e1b0c079019a4ed27771d40a7eed8
    Signed-off-by: Jing Zhang <jing.c.zhang@nokia.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 4f842b4..39494c0 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 4f842b4a7cedcc5ba89542955bf2b64c3451361d
+Subproject commit 39494c01b49cafd893982d74e030b9b96b5fa821