Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  - change openrc file path to /etc/yardstick/openstack.creds

    JIRA: YARDSTICK-623

    Now almost yardstick openrc file is in /etc/yardstick/openstack.creds.
    But only in prepare_env.sh it is /home/opnfv/openrc.
    So I unified it and change it to /etc/yardstick/openstack.creds in the
    follow patch:
    https://gerrit.opnfv.org/gerrit/#/c/32005/
    Also there is some adapt work to do in releng.

    Change-Id: I7764582dec1d9a8f74e53b23e23d98021a20589b
    Signed-off-by: chenjiankun <chenjiankun1@huawei.com>