Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "[docs] Remove vtc results chapter and references"
  - [docs] Remove vtc results chapter and references

    The vTC chapter in the userguide was previously removed [1]
    Some references and results still remained and needed to be removed.

    [1] https://gerrit.opnfv.org/gerrit/gitweb?p=yardstick.git;a=commit;h=114a486558c96152fffb5050840460a54de64d15

    JIRA: YARDSTICK-1335
    Change-Id: I17806d90ae8bc4dbf813ef89bbc22dc012b4a686
    Signed-off-by: Emma Foley <emma.l.foley@intel.com>