build: Update etcd dependency
build: Update etcd dependency

Notable changes include coreos/etcd#6286 (which fixes the issue that was
preventing us from upgrading sooner), and coreos/etcd#5809 (which fixes
a possible cause of failed leader transfers discussed in #8834)

Fixes #8017

glycerine/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,glycerine/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,paperstreet/cockroach,petermattis/cockroach,paperstreet/cockroach,maxlang/cockroach,petermattis/cockroach,veteranlu/cockroach,veteranlu/cockroach,veteranlu/cockroach,cockroachdb/cockroach,petermattis/cockroach,paperstreet/cockroach,glycerine/cockroach,vaibhavarora/cockroach,maxlang/cockroach,petermattis/cockroach,cockroachdb/cockroach,cockroachdb/cockroach,petermattis/cockroach,maxlang/cockroach,maxlang/cockroach,petermattis/cockroach,glycerine/cockroach,veteranlu/cockroach,veteranlu/cockroach,paperstreet/cockroach,veteranlu/cockroach,petermattis/cockroach,petermattis/cockroach,maxlang/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,glycerine/cockroach,maxlang/cockroach,paperstreet/cockroach,cockroachdb/cockroach,maxlang/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,glycerine/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,vaibhavarora/cockroach,maxlang/cockroach,cockroachdb/cockroach,cockroachdb/cockroach,glycerine/cockroach,glycerine/cockroach