Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Prox vnf descriptor cleanup"
  - Prox vnf descriptor cleanup

    JIRA: YARDSTICK-1003

    - There are redundant files for Prox vnf descriptors
    tg and vnf for 1, 2 and 4 port set-up.
    - We can use one vnf descriptor file per prox tg and prox vnf,
    reducing the number of redundant files.
    - Tested on Prox BM L2fwd 2 and 4 port test case.

    Change-Id: I4c61fd11725121f19392443460ac2ad39c934e2d
    Signed-off-by: Abhijit Sinha <abhijit.sinha@intel.com>