XForceExchange: Not handling errors

Original Report: https://gitter.im/MISP/Support?at=5e5acf064eefc06dcf27f477

 2020-02-28 14:33:38,855 - misp-modules - ERROR - Something went wrong:
 Traceback (most recent call last):
   File "/usr/local/lib/python3.7/site-packages/misp_modules/__init__.py", line 201, in post
     response = yield tornado.gen.with_timeout(timeout, self.run_request(jsonpayload))
   File "/usr/local/lib/python3.7/site-packages/tornado/gen.py", line 735, in run
     value = future.result()
   File "/usr/local/lib/python3.7/concurrent/futures/thread.py", line 57, in run
     result = self.fn(*self.args, **self.kwargs)
   File "/usr/local/lib/python3.7/site-packages/misp_modules/__init__.py", line 189, in run_request
     response = mhandlers[x['module']].handler(q=jsonpayload)
   File "modules/expansion/xforceexchange.py", line 164, in handler
     parser.parse()
   File "modules/expansion/xforceexchange.py", line 43, in parse
     getattr(self, to_call)(self.attribute.value)
   File "modules/expansion/xforceexchange.py", line 125, in _parse_ip
     self._parse_dns(value)
   File "modules/expansion/xforceexchange.py", line 108, in _parse_dns
     if dns_result.get('Passive') and dns_result['Passive'].get('records'):
 AttributeError: 'NoneType' object has no attribute 'get'

https://github.com/MISP/misp-modules/blob/master/misp_modules/modules/expansion/xforceexchange.py#L107-L108

_api_call can return NoneType either via exception, or non 200 HTTP code. This problem appears to be not handled in all calls to _api_call

I do not have an API key to even test this, so can't even begin to figure out the solution.

Start in misp_modules/modules/expansion/xforceexchange.py, especially _api_call and the _parse_dns traceback around lines 107-108. Review every shown call site for exception and non-200 responses, then verify that failed API responses no longer produce the reported NoneType AttributeError.