misc/dashboard: show all race builders as "race"

race is more important than arch (moreover race implies x64)
don't know how to test it

R=golang-dev, dave, r
CC=golang-dev
https://golang.org/cl/10484046

misc/dashboard/app/build/ui.go

@@ -211,7 +211,7 @@ func builderArch(s string) string {
 
 // builderArchShort returns a short arch tag for a builder string
 func builderArchShort(s string) string {
-	if s == "linux-amd64-race" {
+	if strings.Contains(s+"-", "-race-") {
 		return "race"
 	}
 	arch := builderArch(s)