use new close method for disconnecting where we can

lib/active_record/connection_adapters/mysql2_adapter.rb

@@ -243,10 +243,12 @@ module ActiveRecord
       end
 
       def disconnect!
+        @connection.close
         @connection = nil
       end
 
       def reset!
+        disconnect!
         @connection = Mysql2::Client.new(@config)
       end
 

lib/sequel/adapters/mysql2.rb

@@ -150,7 +150,7 @@ module Sequel
 
       # Closes given database connection.
       def disconnect_connection(c)
-        c = nil
+        c.close
       end
 
       # Convert tinyint(1) type to boolean if convert_tinyint_to_bool is true