Automatic merge from submit-queue

Move HighWaterMark to the top of the struct in order to fix arm

I haven't tested this yet, but let's see how e2e tests react.
It should be no difference at all except for that it will fix arm.

etcd has had to do this some times (and I think there are some fixes like this that are needed for etcd as well)

For reference see: https://golang.org/pkg/sync/atomic/

This should be a cherrypick-candidate for v1.4.1 (as I understand it, v1.4.0 has clearly left the cherrypickable state)

@lavalamp @pwittrock @xiang90 @smarterclayton