sweet/benchmarks/internal/driver: use new diagnostics framework

Change-Id: I95ba76c5865c416fd768f1a5f0c1cfeeb8c997e7
Cq-Include-Trybots: luci.golang.try:x_benchmarks-gotip-linux-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/600069
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>