storage: avoid processing replicas concurrently in a queue
storage: avoid processing replicas concurrently in a queue

See #8794.

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