Update git submodules

Update git submodules

* Update docs/submodules/samplevnf from branch 'master'
  - Merge "Add support for multiple variables in core definition"
  - Add support for multiple variables in core definition

    In the [core] definition we were able to use one variable
    such as $core1 in [core $core1] but not [core ${core1}].
    The second syntax is used when we want multiple
    variables such as in [core ${first_core}-${last_core}].
    This second syntax is now supported.

    Change-Id: Ic94b84cb8cf827acb6697789cd180f41c3bdb028
    Signed-off-by: Xavier Simonart <xavier.simonart@intel.com>