Refactor tests to stop sharing global models between different test suites and use local per-app model registry instead. Also clean up all test code to use `const` and `let` instead of `var`.
- Refactor some tests to use bluebird for promise impl - Fix based on comments at https://github.com/strongloop/loopback-connector-remote/pull/44/files#r61875179 - Add tests to integration dir (organized/named by feature)