Improve creating and deleting of shard_db docs
Improve creating and deleting of shard_db docs

When creating a db detect conflicts when writing
the shard_db doc and fail. When deleting the shard_db doc
make sure multiple leafs that might occur from deleting and
re-creating the same db are all deleted.

BugzID:12220

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