Update git submodules

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>