Model-specific schema not respected by SQL building methods

[zenflow]

We are working with a legacy database that has our data divided among different schemas.

As per the documentation, I should be able to set the schema for an individual model. https://docs.strongloop.com/display/public/LB/Model+definition+JSON+file#ModeldefinitionJSONfile-Datasource-specificoptions

However, SQLConnector does not specify any schema in the SQL statements that it builds, even though there is a schema method that properly determines which schema to use for a given model.

We should use this schema method to always specify the schema in generated SQL.

@raymondfeng @bajtos What are the chances of this being implemented and released as version 3? It doesn't look like a complicated change, so I could probably implement it myself and submit a PR, if that increases the chances.

Are there any problems you can see with making this change? I know this would break loopback-connector-db2 since it needlessly overrides the schema method with a schema string property in the constructor, which is why I believe it should be released in the next major version.

Thanks :)