Introduce util/obc as the home for ObjectBucketClaim test helpers: the
provisioner StorageClass constructor (moved out of util/fixture, where it
was a misplaced pure constructor), the create/bound and delete/absent
lifecycle waiters, and a per-OBC S3 client. The lifecycle waiters and S3
client are promoted from the notification suite, which built them inline as
their only consumer.
Retarget the StorageClass callers (topic/kafka, bucket/owner) and rework
the notification suite onto the shared helpers.
Signed-off-by: Joshua Hoblitt <josh@hoblitt.com>