Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'stable/danube'
  - Yardstick virtualenv support

    JIRA: YARDSTICK-620

    In the patch, I separate python-setuptools from install.sh
    and separate appdirs from requirements.txt because there will be
    error when install them in virtualenv.
    Also I will update the documentation when this patch merged;

    Change-Id: I99a532d1851983775869e7c5e8e65fd0229e86df
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>
    (cherry picked from commit bb365d411d88a71871993b4ed803c2ffbbcb79bf)