Update git submodules

* Update docs/submodules/ccsdk/platform/plugins.git from branch 'master'
  to 556b233513db587f5d3982628dbca200fd3a9e2a
  - DMaaP add support for useExisting
    
    Issue-ID: DCAEGEN2-1670
    Signed-off-by: Jack Lucas <jflucas@research.att.com>
    Change-Id: I0a945117b7f4084191245ea56af2712b2cd20d4c
    
1 file changed