allow user add needUpdate func in cluster/machine provider

[leoryu]

allow add provider needupdate func in this place.

[TomatoAres]

Design:

1. We add a NeedUpdate method in provider，which could be implemented by user;
2. Platform controller and provider all judge needUpdate, if one of judgement result is deny, then we don't update;
3. The needUpdate of provider exist now all return false;