Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'stable/fraser'
  - Implement Virtual Switch resilience test case

    This testcase tests the resilience of the Virtual
    Switch in an OpenStack environment. It can only run in a
    non Ubuntu distro because it is limited by this bug [0]

    [0]: JIRA: YARDSTICK-1140

    Change-Id: Ia1480fba9f3549d1144c80699056b501d3b07a0f
    Signed-off-by: Dimitrios Markou <mardim@intracom-telecom.com>
    (cherry picked from commit 53f5951a47fcaa5a3f8bcd6ea1020e54a1b285d3)