Replace embedded adapter SQL with macros

[beckjake]

Feature

dbt should not have embedded SQL in adapter code. Instead, those things should just be written as macros that pass any necessary information into execute_macro

Feature description

There are quite a few places in dbt where queries to the information schema, etc are hardcoded as format()'able strings inside adapter methods. With the new execute_macro behavior, it should be super easy to directly translate those into macros!

Who will this benefit?

This will make it easier to leverage dbt's macro/adapter_macro system for writing new adapters. Currently you have to embed SQL into the adapter in some places and macros in other places, it's not very consistent or predictable.