json-c: Add ptest for json-c

json-c: Add ptest for json-c

Adapt json-c recipe to compile and deploy a ptest for json-c.
Also add a small script for executing the tests.
All tests were successful on a trial and took around 20 seconds.

Signed-off-by: Simone Weiß <simone.weiss@elektrobit.com>
Signed-off-by: Kai Tomerius <kai.tomerius@elektrobit.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>