Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Fix RabbitMQ service installation and initialization"
  - Fix RabbitMQ service installation and initialization

    RabbitMQ service added in [1] is not correctly installed and initialized:
    - There is an error during the installation process ("\" character
      missing).
    - In the installation script, the service needs to be started first.
    - In the container installation, the service needs to be started via
      supervisor.

    [1]https://gerrit.opnfv.org/gerrit/#/c/53597/

    JIRA: YARDSTICK-1103

    Change-Id: Iade3d6ce4b522e6f576af71b7afe5559081f7929
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>