Json matcher small bug

[ipmach]

Bug in JsonParser json_parser.py line 61:

content_parser_name = config.get("content_parser", "JsonMatcherParser")

should be something like:

content_parser_name = config["parsers"][name].get("content_parser", "JsonMatcherParser")

Currently the line is always assigning "JsonMatcherParser" to content_parser_name as it can not reach the actual place of the field in the config dict.