Add JSON Should Contain Sub JSON Keyword

This patch provides functionality of "Dictionary Should Contain Sub
Dictionary" Keyword (from Robot Framework "Collections" library) for
JSON. It supports both objects and strings containing JSON.

Added tests were intended to verify no regressions were introduced as
well as corner cases are handled properly.

Issue-ID: SECCOM-261
Change-Id: Id7581d79b93ce0403e97e1bbf47c10e0e166f2ec
Signed-off-by: Pawel Wieczorek <p.wieczorek2@samsung.com>
3 files changed