virt-who ログに "Server error attempting a POST to /rhsm/hypervisors?owner=ORG&env=ENV returned status 500" が記録される

Issue

virt-who サーバーは RHSM 経由で Satellite 6 にレポートできるはずですが、以下のトレースバックが virt-who ログに記録されます。

2016-03-21 11:03:06,378 [ERROR]  @virtwho.py:123 - Error in communication with subscription manager:
Traceback (most recent call last):
  File "/usr/share/virt-who/virtwho.py", line 107, in send
    self._sendGuestAssociation(report)
  File "/usr/share/virt-who/virtwho.py", line 134, in _sendGuestAssociation
    result=manager.hypervisorCheckIn(report.config, report.association, report.config.type)
  File "/usr/share/virt-who/manager/subscriptionmanager/subscriptionmanager.py", line 152, in hypervisorCheckIn
    return self.connection.hypervisorCheckIn(config.owner, config.env, serialized_mapping)
  File "/usr/lib64/python2.6/site-packages/rhsm/connection.py", line 815, in hypervisorCheckIn
    return self.conn.request_post(url, host_guest_mapping)
  File "/usr/lib64/python2.6/site-packages/rhsm/connection.py", line 605, in request_post
    return self._request("POST", method, params)
  File "/usr/lib64/python2.6/site-packages/rhsm/connection.py", line 530, in _request
    self.validateResponse(result, request_type, handler)
  File "/usr/lib64/python2.6/site-packages/rhsm/connection.py", line 578, in validateResponse
    handler=handler)
RemoteServerException: Server error attempting a POST to /rhsm/hypervisors?owner=ORG&env=Library returned status 500