cam-image,test: Add tcpdump support to Pytest

Add tcpdump support to the Pytest tests by the optional parameter
--with-tcpdump, when it is passed with the path to the tcpdump
binary, it enables its usage in order to capture the packets
exchanged between the cam-app-example and the cam-service, saving
the data to perform analysis in case of issues.

Install tcpdump in the Linux container, update the documentation,
update codeclimate structure checker to allow 6 parameters,
because Pytest framework needs that amount.

Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>