Automatic merge from submit-queue

Use etcd 2.3.7

This will switch to etcd 2.3.7 for release 1.4, to resolve issues rolling back from 1.4 to 1.3 (while preventing those same issues rolling back to 1.4.0 from a release including etcd 3.0.x).

Fixes #32253.

See #32253 (comment) for etcd roadmap.