Refactoring message_sever integration test

[da1suk8]

• The comparison of events is difficult to understand, so we would like to make it easier to understand by using the utility function or other means.
  

  wasmd/x/wasm/keeper/msg_server_integration_test.go

  Line 42 in 9c983a9

  // check event

• change to use Unmarshal data response

  wasmd/x/wasm/keeper/msg_server_integration_test.go

  Line 136 in bb3a88f

  assert.Contains(t, string(rsp.Data), string(events[1].Attributes[0].Value))

  
  FYI:

  wasmd/x/wasm/keeper/msg_server_integration_test.go

  Lines 208 to 209 in bb3a88f

  	var instantiateResponse types.MsgInstantiateContractResponse
  	require.NoError(t, wasmApp.AppCodec().Unmarshal(rsp.Data, &instantiateResponse))

• For attributes and events that are specific to a contract, we would like to add comments to make them easier to understand.