Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Bugfix: openstack router list broken in Yardstick container - dovetail"
  - Bugfix: openstack router list broken in Yardstick container - dovetail

    Dependancy of python-openstackclient is not constrained.
    This patch specify openstacksdk and openstackclient's version according to [1].

    This patch apply for bugfix and need to backported to fraser stable branch.
    Continual work need to be done in Gambia according to YARDSTICK-1398.

    [1]
    https://github.com/openstack/requirements/blob/stable/pike/upper-constraints.txt

    JIRA: DOVETAIL-728

    Change-Id: I57c718e192699ac322150458d18508b06c93d22b
    Signed-off-by: rexlee8776 <limingjiang@huawei.com>