Update git submodules

Update git submodules

* Update docs/submodules/samplevnf from branch 'stable/gambia'
  - Test improvements and fixes for image creation

    Updated and corrected the creation of an image containing the PROX
    tool with packer.
    Test will now only be declared successful when average and maximum
    latency are below a certain threshold.
    The start speed is now also a parameter of the *.test files.

    Change-Id: I1112555c87e7a857e1c699921ae08f61281642e1
    Signed-off-by: Luc Provoost <luc.provoost@intel.com>