correct bucket_name to bucket.name

[dwo]

I had written something thinking it should be

buckets = client.list_buckets()
bucket_set = set([bucket.bucket_name for bucket in buckets])

but I actually had to write

buckets = client.list_buckets()
bucket_set = set([bucket.name for bucket in buckets])

[dwo]

sorry, probably should have [ci skip]'d this 🙊

[harshavardhana]

Thanks for the PR @dwo