Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Remove TRex installer from ansible directory"
  - Remove TRex installer from ansible directory

    Standalone TRex installer script is not updated or maintained.
    TRex is installed in Jumphost and the physical nodes using the
    installer script. There is no need to keep this script anymore.

    JIRA: YARDSTICK-1251

    Change-Id: I3af62e70e244d2277a980a1ca6b8079597621a62
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>