Unavailable attribute causes 'Unknown error'

[jkakavas]

If an attribute has been defined in the hash dictionary in the configuration and this attribute is not available for a given transaction, this causes SAtoSA to fail with an 'Unknown error'

The stacktrace is as follows:

[2017-04-28 07:48:24] [ERROR]: Unknown error
Traceback (most recent call last):
  File "/home/debian/vopaas/virtualenv/lib/python3.4/site-packages/satosa/base.py", line 255, in run
    resp = self._run_bound_endpoint(context, spec)
  File "/home/debian/vopaas/virtualenv/lib/python3.4/site-packages/satosa/base.py", line 203, in _run_bound_endpoint
    return spec(context)
  File "/home/debian/vopaas/virtualenv/lib/python3.4/site-packages/satosa/micro_services/consent.py", line 79, in _handle_consent_response
    return self._end_consent(context, internal_response)
  File "/home/debian/vopaas/virtualenv/lib/python3.4/site-packages/satosa/micro_services/consent.py", line 218, in _end_consent
    return super().process(context, internal_response)
  File "/home/debian/vopaas/virtualenv/lib/python3.4/site-packages/satosa/micro_services/base.py", line 33, in process
    return self.next(context, data)
  File "/home/debian/vopaas/virtualenv/lib/python3.4/site-packages/satosa/base.py", line 139, in _auth_resp_finish
    for v in internal_attributes[attribute]]
KeyError: 'edupersonprincipalname'

This happens because an assumption has been made that if a attribute is configured for hashing, it will always be available.