Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Refactor remote command execution in pktgen"
  - Refactor remote command execution in pktgen

    Some remote commands in Pktgen are executed without checking the exit
    status. This patch makes all remote commands check exit value, and
    removes unused variables that are captured from remote command
    executions.

    JIRA: YARDSTICK-1166

    Change-Id: I42a667ebd22d086887d61e1671bc569b03c59d33
    Signed-off-by: Miikka Koistinen <miikka.koistinen@nokia.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index d64760d..c9b1716 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit d64760d051ec14002847352a20da02774a8bda05
+Subproject commit c9b1716fd37284d09b4c327b65fd5d7c8769fc7f