sql: pad the keys more in kv_test.go
sql: pad the keys more in kv_test.go

If the code gets faster, the benchmark starts failing because the keys no longer
sort lexicographically like the test assumes.

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