cmd/coordinator: try to use gitmirror in staging
cmd/coordinator: try to use gitmirror in staging

Change-Id: Ic57bcb07a5091c1efc3621fcbdccfc7a19505f79
Reviewed-on: https://go-review.googlesource.com/38749
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build