Changes

esim/http_json_api: add alternative API interface

unfortunately the API changes introduced in change

I277aa90fddb5171c4bf6c3436259aa371d30d092

broke the API interface of http_json_api.py. This was taken into
account and necessary to introduce add the server functionality next
to the already existing client functionality. The changes to the API
were minimal and all code locations that use http_json_api.py
were re-aligned.

Unfortunately it was not clear at this point in time that there are
out-of-tree projects that could be affected by API changes in
http_json_api.py

To mitigate the problem this patch introduces an alternative API
interface to the JsonHttpApiFunction base class. This alternative
API interface works like the old API interface when the class is
instantiated in the original way. To make use of the revised client
the API use has to pass an additional keyword argument that defines
the role.

Related: SYS#7866
Change-Id: I2a5d4b59b12e08d5eae7a1215814d3a69c8921f6