storage/db/dbtest: fix -cloud after refactoring
storage/db/dbtest: fix -cloud after refactoring

Change-Id: I7bd1ed03127830d6530415d77263ee8b0155a2c4
Reviewed-on: https://go-review.googlesource.com/37230
Run-TryBot: Quentin Smith <d6b8e48afb2534b213e391cab43016505747a234@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

golang/perf,golang/perf