[iot] `identity_assignment` is called on another thread

[jiasli]

I discovered a problem with iot module:

azure-cli/src/azure-cli/azure/cli/command_modules/iot/custom.py

Lines 588 to 590 in 9ef066f

	create = client.iot_hub_resource.begin_create_or_update(resource_group_name, hub_name, hub_description, polling=True)
	if identity_role and identity_scopes:
	create.add_done_callback(identity_assignment)

polling=True causes SDK to start a separate thread to do the LRO polling. Even if identity_assignment fails, it fails in that separate thread, so the main thread running the CLI command still succeeds, which is not expected.

Originally posted by @jiasli in #25452 (comment)

[yonzhan]

route to service team

[jiasli]

Please also see #17185

[vilit1]

Merged. closing issue