test: limit runoutput concurrency with -v

This appears to have simply been an oversight.

Change-Id: Ia5d1309b3ebc99c9abbf0282397693272d8178aa
Reviewed-on: https://go-review.googlesource.com/c/142885
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

test/run.go

@@ -78,6 +78,7 @@ func main() {
 	// Disable parallelism if printing or if using a simulator.
 	if *verbose || len(findExecCmd()) > 0 {
 		*numParallel = 1
+		*runoutputLimit = 1
 	}
 
 	ratec = make(chan bool, *numParallel)