Zero out shard caches on upgrade
Zero out shard caches on upgrade

The mix of #shard and #ordered_shard records breaks ushards.  Different
nodes can start returning different results.

fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb