Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Bugfix: Can't get image list in API"
  - Bugfix: Can't get image list in API

    JIRA: YARDSTICK-1110

    To match OpenStack Pike release, we upgrade novaclient from 7.1.1 to 9.1.1.
    And the client interface has changed, it no longer has nova_client.images attribute.
    So I use shade instead. Later will change all same issue.

    Change-Id: Ie4f54069d4346e44e2ad925439930504b945cbad
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>