Schema cache: Lazy creation of buckets and related zookeeper nodes

[evert]

When Lily is started, 256 buckets are created and the related zookeeper nodes are created. When not a lot of types are created in the schema this results in a redundant amount of buckets.
In this case we could consider not to create the buckets and zookeeper nodes at startup, but create them when needed. This would gain some speed at startup and full schema cache refresh.
But when there are not a lot of types, this schema cache refresh speed is not really an issue.
So the complexity that this would introduce is currently not considered worth the gain.