Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'stable/fraser'
  - Merge "Remove instantiated contexts in "test_task"" into stable/fraser
  - Remove instantiated contexts in "test_task"

    During unit testing, all contexts instantiated must be deleted at the end
    of the test to avoid clashes with other tests.

    JIRA: YARDSTICK-1209

    Change-Id: I1994b915001b4a518e096833a0c5d33febbd8de6
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>
    (cherry picked from commit 5e4d95ba299ce92588701d9481657c343b8ef609)