Automatic merge from submit-queue

Use uid in config.go instead of pod full name.

For https://github.com/kubernetes/kubernetes/issues/43397.

In config.go, use pod uid in pod cache.

Previously, if we update the static pod, even though a new UID is generated in file.go, config.go will only reference the pod with pod full name, and never update the pod UID in the internal cache. This causes:
1) If we change container spec, kubelet will restart the corresponding container because the container hash is changed.
2) If we change pod spec, kubelet will do nothing.

With this fix, kubelet will always restart pod whenever pod spec (including container spec) is changed.

@yujuhong @bowei @dchen1107 
/cc @kubernetes/sig-node-bugs