storage: Store.updateReplicationGauges will now hold the store lock for less time
storage: Store.updateReplicationGauges will now hold the store lock for less time

Closes #9261

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