Json to composite node test

contains tests for:
- elements leaf, leaf list, list, container under list or container
- json top level elements check
- check of read empty simple data like leaf, leaf list

Change-Id: I6826cb32415fc135eb7f966f7325c5d15e21ac1a
Signed-off-by: Jozef Gloncak <jgloncak@cisco.com>