s3api logging causes 500 when setting ACLs with empty ID

[Tim Burke]

Seen when testing locally:

Dec 13 17:13:05 saio proxy-server: __str__ returned non-string (type NoneType):
Traceback (most recent call last):
  File "/vagrant/swift/swift/common/middleware/s3api/s3api.py", line 345, in __call__
    resp = self.handle_request(req)
  File "/vagrant/swift/swift/common/middleware/s3api/s3api.py", line 383, in handle_request
    res = handler(req)
  File "/vagrant/swift/swift/common/middleware/s3api/controllers/s3_acl.py", line 65, in PUT
    req.get_response(self.app, 'POST')
  File "/vagrant/swift/swift/common/middleware/s3api/s3request.py", line 1615, in get_response
    resp = self.acl_handler.handle_acl(
  File "/vagrant/swift/swift/common/middleware/s3api/acl_handlers.py", line 94, in handle_acl
    return getattr(ah, method)(app)
  File "/vagrant/swift/swift/common/middleware/s3api/acl_handlers.py", line 291, in POST
    'Grant %s %s permission on the bucket /%s' %
TypeError: __str__ returned non-string (type NoneType)

Trouble comes down to how Users get str()ed: https://github.com/openstack/swift/blob/2.30.0/swift/common/middleware/s3api/subresource.py#L221-L222

The display_name passed to the constructor (apparently) may be None, causing __str__ to return None, causing the TypeError.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/swift/+/869401