Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Revert "vPE Sample VNF is missing in the installation scripts""
  - Revert "vPE Sample VNF is missing in the installation scripts"

    SampleVNF source tree doesn't contain vPE VNF sources, thus the
    installation of the vPE sampleVNF fails because of the changes.
    Reverting.

    This reverts commit 5bb855a82d960a4fb796e801ec9a9a22dc40b1ca.

    Change-Id: I27e929e813a28847c2ca725031ec767633a36954
    Signed-off-by: Mytnyk, Volodymyr <volodymyrx.mytnyk@intel.com>