Update git submodules

Update git submodules

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

    * Remove unneeded variables
    * Do not raise RuntimeError when a remote command fails, instead
      leave it for the yardstick ssh module to handle.
    * Prevent CsvReader from raising StopIteration if csv output cannot be
      parsed. The SLA validation will take care of errors in that case.

    JIRA: YARDSTICK-1166

    Change-Id: I9e353d39dfd3bd27407dde32744ce71b5762e84e
    Signed-off-by: Miikka Koistinen <miikka.koistinen@nokia.com>