IBM FlashSystem driver failing test_force_detach_volume

The IBM FlashSystem driver has been failing test_force_detached_volume since a change was introduced for bug 1619647 that allows users to request force detach with no connector. Here is a log excerpt from a failed run showing the error:

2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager [req-bb867c75-bfad-43e6-a4e8-b3a76ef5248b 52c5e76f87e84c18990197ef4c22eb7b 3dfb6d7e651841a3aa3e689f4e785c65 - default default] Terminate volume connection failed: argument of type 'NoneType' is not iterable: TypeError: argument of type 'NoneType' is not iterable
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager Traceback (most recent call last):
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager File "/usr/lib/python2.7/site-packages/cinder/volume/manager.py", line 1816, in terminate_connection
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager force=force)
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager File "/usr/lib/python2.7/site-packages/oslo_concurrency/lockutils.py", line 274, in inner
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager return f(*args, **kwargs)
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager File "/usr/lib/python2.7/site-packages/cinder/volume/drivers/ibm/flashsystem_fc.py", line 344, in terminate_connection
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager self._unmap_vdisk_from_host(vdisk_name, connector)
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager File "/usr/lib/python2.7/site-packages/oslo_concurrency/lockutils.py", line 274, in inner
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager return f(*args, **kwargs)
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager File "/usr/lib/python2.7/site-packages/cinder/volume/drivers/ibm/flashsystem_common.py", line 902, in _unmap_vdisk_from_host
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager if 'host' in connector:
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager TypeError: argument of type 'NoneType' is not iterable
2019-02-26 15:59:17.942 37 ERROR cinder.volume.manager
2019-02-26 15:59:17.943 37 ERROR oslo_messaging.rpc.server [req-bb867c75-bfad-43e6-a4e8-b3a76ef5248b 52c5e76f87e84c18990197ef4c22eb7b 3dfb6d7e651841a3aa3e689f4e785c65 - default default] Exception during message handling: VolumeBackendAPIException: Bad or unexpected response from the storage volume backend API: Terminate volume connection failed: argument of type 'NoneType' is not iterable
2019-02-26 15:59:17.943 37 ERROR oslo_messaging.rpc.server Traceback (most recent call last):
2019-02-26 15:59:17.943 37 ERROR oslo_messaging.rpc.server File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/server.py", line 163, in _process_incoming
2019-02-26 15:59:17.943 37 ERROR oslo_messaging.rpc.server res = self.dispatcher.dispatch(message)
2019-02-26 15:59:17.943 37 ERROR oslo_messaging.rpc.server File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/dispatcher.py", line 265, in dispatch
2019-02-26 15:59:17.943 37 ERROR oslo_messaging.rpc.server return self._do_dispatch(endpoint, method, ctxt, args)
2019-02-26 15:59:17.943 37 ERROR oslo_messaging.rpc.server File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/dispatcher.py", line 194, in _do_dispatch
2019-02-26 15:59:17.943 37 ERROR oslo_messaging.rpc.server result = func(ctxt, **new_args)
2019-02-26 15:59:17.943 37 ERROR oslo_messaging.rpc.server File "/usr/lib/python2.7/site-packages/cinder/volume/manager.py", line 1821, in terminate_connection
2019-02-26 15:59:17.943 37 ERROR oslo_messaging.rpc.server raise exception.VolumeBackendAPIException(data=err_msg)
2019-02-26 15:59:17.943 37 ERROR oslo_messaging.rpc.server VolumeBackendAPIException: Bad or unexpected response from the storage volume backend API: Terminate volume connection failed: argument of type 'NoneType' is not iterable

The driver needs to be changed to produce the expected response in this scenario, which is to destroy all the volume's attachments.