Reduce SchemaFactory to generating a new AIS or working on an existing one. Remove generation of partial AIS based on existing one.
Make ApiTestBase just use DDL in the ordinary way for its operations, rather than a third instance of Table/Index/... via SchemaFactory.
merge MMcM: Simplify SchemaFactory contract

Merge pull request #1003 from MMcM/sql-layer/schema-factory-simplify
https://github.com/FoundationDB/sql-layer/pull/1003