Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Module to manage pip packages"
  - Module to manage pip packages

    This new module provides methods to manage Python PIP packages from
    a URL, from a local directory or from a build PIP package.

    The implemented commands are:
    - Install package.
    - Remove package.
    - List all installed packages in the system.

    JIRA: YARDSTICK-910

    Change-Id: I8f7d1b77c0c384b801cc6f5e67d8b45ce7c6bfdf
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>