The WORM suite creates one bucket per test, each backed by ~3 reserved
volumes on the data node. With ~30 tests and the default `weed mini`
volume cap, the data node runs out of slots midway through the run and
every PutObject after that fails with InternalError.
Hook a sweep of every test-prefix bucket into the create helpers so a
panicked or interrupted prior test cannot leak buckets into the next.
363d5caa85