Drop DB connections between integration tests

Some tests set up state which is used to initialize connections. If that initialization happens when the pool is populated, the pool will be poisoned with misconfigured connections, and the tests will fail.

Fixes #84.

spec/spec_helper.rb

@@ -48,7 +48,10 @@
   # Cleans up the database before each example, so the current example doesn't
   # see the state of the previous one
   config.before(:each) do |example|
-    test_database.setup if example.metadata[:integration]
+    if example.metadata[:integration]
+      test_database.setup
+      ActiveRecord::Base.connection_pool.disconnect!
+    end
   end
 
   config.order = :random