Add bucket type/index n_val equivalency validator

Registers a create/update bucket type property validator for yokozuna. This ensures that setting properties on a bucket type will validate that 1) the index exists, and 2) the bucket types n_val equals the index's n_val.

This forced a change to the tests, whereby an index must first be created, then `wait_for_index`, then associate the index with the bucket. Before this check, waiting didn't matter until values were written.