Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Install RabitMQ for RPC messaging between processes"
  - Install RabitMQ for RPC messaging between processes

    In NetworkServices Tescases, the TGs (traffic generators) run the traffic in
    a separate process. In order to synchronize the traffic injection and the
    runner interval loops, an RPC server is needed to publish/subscribe events.

    RabbitMQ is a well supported MQ in Linux (used in OpenStack or collectd)
    and supported by Python implemented projects like oslo.messaging [1].

    RabbitMQ default configuration:
    - Port: 5672
    - User/password: yardstick/yardstick

    [1]https://github.com/openstack/oslo.messaging

    JIRA: YARDSTICK-1068

    Change-Id: I15db294ee430fb38e574a59b9ce1bf0f8b651a67
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>