Refactor RSpec for AnnotateModels - structuralize test cases (ctran#755)

The test cases of AnnotateModels.get_schema_info was separated into two sections. So I merged them into one, and refactor test cases. This PR is new version of ctran#741.

Author: nard-tech

.rubocop_todo.yml

@@ -1,6 +1,6 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config`
-# on 2020-02-12 18:43:06 +0900 using RuboCop version 0.68.1.
+# on 2020-02-13 18:10:52 +0900 using RuboCop version 0.68.1.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
@@ -528,7 +528,7 @@ Style/UnneededPercentQ:
  Exclude:
  - 'annotate.gemspec'
 
-# Offense count: 344
+# Offense count: 346
 # Cop supports --auto-correct.
 # Configuration parameters: AutoCorrect, AllowHeredoc, AllowURI, URISchemes, IgnoreCopDirectives, IgnoredPatterns.
 # URISchemes: http, https