use teardown for cleanup, not setup.

This solves order dependent issues where the last test
leaked the query cache state. This resulted in the following error:

```
QueryCacheExpiryTest#test_cache_is_expired_by_habtm_delete [test/cases/query_cache_test.rb:275]:
not all expectations were satisfied
unsatisfied expectations:
- expected exactly twice, invoked once: #<ActiveRecord::ConnectionAdapters::SQLite3Adapter:0x7f93e0c65838>.clear_query_cache(any_parameters)
```

activerecord/test/cases/query_cache_test.rb

@@ -8,7 +8,7 @@
 class QueryCacheTest < ActiveRecord::TestCase
   fixtures :tasks, :topics, :categories, :posts, :categories_posts
 
-  def setup
+  teardown do
     Task.connection.clear_query_cache
     ActiveRecord::Base.connection.disable_query_cache!
   end
@@ -214,7 +214,7 @@ def test_cache_gets_cleared_after_migration
     Post.find(1)
 
     # change the column definition
-    Post.connection.change_column :posts, :title, :string, :limit => 80
+    Post.connection.change_column :posts, :title, :string, limit: 80
     assert_nothing_raised { Post.find(1) }
 
     # restore the old definition
@@ -241,7 +241,6 @@ def test_find
 
   def test_update
     Task.connection.expects(:clear_query_cache).times(2)
-
     Task.cache do
       task = Task.find(1)
       task.starting = Time.now.utc
@@ -251,7 +250,6 @@ def test_update
 
   def test_destroy
     Task.connection.expects(:clear_query_cache).times(2)
-
     Task.cache do
       Task.find(1).destroy
     end
@@ -259,7 +257,6 @@ def test_destroy
 
   def test_insert
     ActiveRecord::Base.connection.expects(:clear_query_cache).times(2)
-
     Task.cache do
       Task.create!
     end