Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Test case spec for SDN Virtual Switch resilience."
  - Test case spec for SDN Virtual Switch resilience.

    This is a test case for verifying the proper functionality of
    SDN Vswitches which are located in the Compute nodes of an OpenStack
    environment.
    This test case is unaware of the configuration (non-HA,HA)

    JIRA: HA-34
    JIRA: YARDSTICK-955

    Change-Id: I701bf1f9527b1a31b9cb52e102734e10c4162766
    Signed-off-by: Dimitrios Markou <mardim@intracom-telecom.com>