storage: explain multiTestContext stopping subtleties
storage: explain multiTestContext stopping subtleties

Also simplify the code a bit while I'm here.

petermattis/cockroach,petermattis/cockroach,cockroachdb/cockroach,maxlang/cockroach,arjun4084346/cockroach,arjun4084346/cockroach,glycerine/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,petermattis/cockroach,paperstreet/cockroach,cockroachdb/cockroach,glycerine/cockroach,veteranlu/cockroach,veteranlu/cockroach,paperstreet/cockroach,glycerine/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,arjun4084346/cockroach,cockroachdb/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,vaibhavarora/cockroach,sunya123/cockroach,petermattis/cockroach,maxlang/cockroach,petermattis/cockroach,maxlang/cockroach,sunya123/cockroach,paperstreet/cockroach,sunya123/cockroach,cockroachdb/cockroach,glycerine/cockroach,arjun4084346/cockroach,sunya123/cockroach,paperstreet/cockroach,sunya123/cockroach,arjun4084346/cockroach,veteranlu/cockroach,sunya123/cockroach,vaibhavarora/cockroach,petermattis/cockroach,paperstreet/cockroach,maxlang/cockroach,cockroachdb/cockroach,petermattis/cockroach,veteranlu/cockroach,arjun4084346/cockroach,petermattis/cockroach,glycerine/cockroach,maxlang/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,maxlang/cockroach,paperstreet/cockroach,paperstreet/cockroach,glycerine/cockroach,arjun4084346/cockroach,arjun4084346/cockroach,glycerine/cockroach,veteranlu/cockroach,maxlang/cockroach,veteranlu/cockroach,maxlang/cockroach,vaibhavarora/cockroach,glycerine/cockroach,sunya123/cockroach,sunya123/cockroach,vaibhavarora/cockroach,veteranlu/cockroach