Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Bugfix: remove ping package for it is GPL license

    JIRA: YARDSTICK-777

    In migrate test case, we use ping to count downtime.
    But ping package is GPL license, so we need remove it.
    Since ping command tool can not set timeout less then 1 second, and the
    downtime is less then 1 second, so we need find another package to replace.
    For now, I find most ping tool is GPL license, so maybe later we need to
    implement ping ourselves.
    And the migrate case can not calculate downtime unless user install ping
    themselves.

    Change-Id: I78cba5e4af9de2e3c0bb16b27570bed951caf440
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>