Passing pod UUID to Kubelet.

We need UUID to indicate the instance of a Pod to make restart work. 
I started from this, but ditch that solution due to the following reasons:

1) It is not name indeed. Name is used to maintain the space uniqueness, not time uniqueness
2) It is harder for me to make backward compatibility for now. We eventually want to refactor the API, which means we might break the compatibility later, but not with this PR. 
3) When taking HTTP request with a running container (for example, run_in_container), the user could pass podname and containername without user-unfriendly UUID here. To hash the UUID and make it part of PodFullName makes this almost impossible.