Update git submodules

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

    PktgenDPDKLatency.run will raise a RuntimeError if a remote command
    fails. This commit makes it use the already existing exception raising
    mechanism in yardstick's ssh client.

    JIRA: YARDSTICK-1166

    Change-Id: I3a3c7691399044b174f5d040c015c9b907b2fe5d
    Signed-off-by: Miikka Koistinen <miikka.koistinen@nokia.com>

diff --git a/docs/submodules/yardstick b/docs/submodules/yardstick
index 4c4edf0..aafc775 160000 (submodule)
--- a/docs/submodules/yardstick
+++ b/docs/submodules/yardstick
@@ -1 +1 @@
-Subproject commit 4c4edf05781b0a7d7368cb29d27ae2e92230c194
+Subproject commit aafc77587072fa1a428d9c9cbec47a15e240a694