cmd/api: work around Windows rename issue on the builders

More cmd/api/run.go hell.

Fixes #9407

Change-Id: If8fb446a2471d6372beb0534c9ab6824029b404c
Reviewed-on: https://go-review.googlesource.com/2054
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Minux Ma <minux@golang.org>