Automatic merge from submit-queue

Reuse fields and labels

This should significantly reduce memory allocations in apiserver in large cluster.
Explanation:
- every kubelet is refreshing watch every 5-10 minutes (this generally is not causing relist - it just renews watch)
- that means, in 5000-node cluster, we are issuing ~10 watches per second
- since we don't have "watch heartbets", the watch is issued from previously received resourceVersion
- to make some assumption, let's assume pods are evenly spread across pods, and writes for them are evenly spread - that means, that a given kubelet is interested in 1 per 5000 pod changes
- with that assumption, each watch, has to process 2500 (on average) previous watch events
- for each of such even, we are currently computing fields.

This PR is fixing this problem.