add a test case of nested vector attributes.

add a test case of nested vector attributes.
Given that OCRepresentation supports 3 depths of attributes, RE has extended its functionality to 3 depths of attributes like OCRepresentation

It means developers are able to make the following structure
{
  "key" : [
             [ [0, 1], [4, 5] ],
             [ [4, 5], [7, 8] ]
          ]
}

This test case checks whether it works correct or not

Change-Id: Id9380faf61ecfb3c43465e2b040a83f1225daa0f
Signed-off-by: Rami Jung <rami.jung@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/2555
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>