Fix dumping structure of mysql 8 database (#493)

Author: joevandyk

integration_test/myxql/storage_test.exs

@@ -166,7 +166,7 @@ defmodule Ecto.Integration.StorageTest do
 
     assert {output, 0} =
              Ecto.Adapters.MyXQL.dump_cmd(
-               ["--no-create-info", "--tables", "schema_migrations"],
+               [],
                [],
                PoolRepo.config()
              )

lib/ecto/adapters/myxql.ex

@@ -429,7 +429,11 @@ defmodule Ecto.Adapters.MyXQL do
 
     database_args =
       if database = opts[:database] do
-        ["--database", database]
+        if cmd == "mysqldump" do
+          ["--databases", database]
+        else
+          ["--database", database]
+        end
       else
         []
       end