s3api storage_domain list should be sorted longest to shortest

[Tim Burke]

If you have multiple storage domains configured and one is a subdomain of another, you get different behavior depending on the order in which you configure them. For example, with

   storage_domain = user1.cluster.domain, cluster.domain

things will work reasonably well (aside from the fact that other users won't be able to access buckets named "user1" with bucket-in-host addressing), but

   storage_domain = cluster.domain, user1.cluster.domain

*won't* work well -- when a request comes in for "bucket.user1.cluster.domain", we interpret it as a request for the bucket "bucket.user1" then reject it for having an invalid bucket name.

This is because we currently track the list of domains in the order configured by the user, then iterate through them until we find one that's a suffix of the requested domain. If we instead sort them from longest to shortest when loading the config, we'll have more consistent behavior that generally works better.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/swift/+/898679