[IBM Storwize] Handling NoneType for mapping attributes during prepare fc consistency group

[Abhinav Shrivastava]

If mapping_attrs is None, treating it a dictionary to extract values throws exception

2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall File "/usr/lib/python3.9/site-packages/cinder/volume/drivers/ibm/storwize_svc/storwize_svc_common.py", line 2403, in prepare_fc_consistgrp_success
2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall if mapping_attrs['status'] == 'prepared':
2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall TypeError: 'NoneType' object is not subscriptable
2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall
2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall During handling of the above exception, another exception occurred:
2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall
2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall Traceback (most recent call last):
2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall File "/usr/lib/python3.9/site-packages/oslo_service/loopingcall.py", line 157, in _run_loop
2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall result = func(*self.args, **self.kw)
2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall File "/usr/lib/python3.9/site-packages/cinder/volume/drivers/ibm/storwize_svc/storwize_svc_common.py", line 1878, in _inner
2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall 'exception': ex.message})
2023-12-05 13:46:25.943 271579 ERROR oslo.service.loopingcall AttributeError: 'TypeError' object has no attribute 'message'

[Abhinav Shrivastava (abshriva)]

Proposed fix: https://review.opendev.org/c/openstack/cinder/+/904496