Refactoring of DatabaseEloquentBuilderTest :

- Replace old PHPUnit mocks by Mockery
- Use consistently Collection instead of mock
- factorize repetitive code in `getMockQueryBuilder()` and `getMockModel()` methods
- use `$builder->getQuery()` instead of `$query = $this->getMockQuery` everywhere for consistency
Add tests for Eloquent Builder
Tested methods : pluck, chunk and lists
Merge pull request #3650 from neoxia/4.1-eloquent-builder-test

Refactoring and more tests in Illuminate\Database\Eloquent\Builder