Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Remove unused methods in SampleVNF"
  - Remove unused methods in SampleVNF

    The following private methods are unused in
    yardstick/network_services/vnf_generic/vnf/sample_vnf.py:SampleVNF

    * _build_ports(self)
    * _get_route_data(self, route_index, route_type)
    * _get_port0localip6(self)
    * _get_port1localip6(self)
    * _get_port0prefixlen6(self)
    * _get_port1prefixlen6(self)
    * _get_port0gateway6(self)
    * _get_port1gateway6(self)

    They are being removed as:
    * _get_port* functions are already implemented and used in MultiPortConfig
    * _get_route_data is an auxillary functions used by the previous ones
    * _build_ports is implemented in the helpers

    JIRA: YARDSTICK-1122
    Change-Id: Ie7a706cd87b610ea56f89214118a02e612a70dc0
    Signed-off-by: Emma Foley <emma.l.foley@intel.com>