Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'stable/gambia'
  - Merge "Add traffic duration support in test case" into stable/gambia
  - Add traffic duration support in test case

    Implement code to support traffic_duration field in test case options.
    This updates the 'duration' in Landslide session profile.
    traffic_duration should always be much less than runner duration/timeout.

    JIRA: YARDSTICK-1427

    Change-Id: I51094bade683ca8758136ccb619e8894a2ecef72
    Signed-off-by: Orest Voznyy <orestx.voznyy@intel.com>
    (cherry picked from commit ae2ceba66519555749c67eefe2170ea716a1411b)