Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "SA: Fix private key file name generation issue"
  - SA: Fix private key file name generation issue

    In current implementation of Yardstick, SA context uses the
    same SSH key file name for each VM created. E.g. the Yardstick
    overrides the key file context each time the new VM is created.
    As a result, the key file is valid only for last VM created
    by Yardstick causing the connection problem for other VMs.
    Solution is to generate different key file name for each VM
    name separately.

    JIRA: YARDSTICK-1436

    Change-Id: I22ae2874695736255aa3314654a2cced9338b53d
    Signed-off-by: Mytnyk, Volodymyr <volodymyrx.mytnyk@intel.com>