Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Change tc_trex files to execute standalone tests"
  - Change tc_trex files to execute standalone tests

    Changes made in test cases for trex TG files to be able to run tests
    for standalone setup (OVS-DPDK/SRIOV).
    - tg__0: trafficgen_1

    Changes to improve templates for tc_trex:
    - flavor: images: changed to default name: yardstick-nsb-image.img
    - default path for files under contexts section
    - RAM size

    JIRA: YARDSTICK-1368

    Change-Id: Ida85de219acd566840de1a94975b8050c7f59b9b
    Signed-off-by: Stepan Andrushko <stepanx.andrushko@intel.com>