all: fix printf(var) mistakes detected by latest printf checker

Used %q instead of %s when reporting an unexpected body to make
potential non-printable characters easier to see.

For golang/go#69267.

Change-Id: Ice78a175df5770afd20189b93c9659b9e966c9bb
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/610915
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Tim King <taking@google.com>

http/http.go

@@ -56,7 +56,7 @@ func makeOneRequest() bool {
 		log.Fatalf("ReadAll: %v", err)
 	}
 	if s := string(b); s != "Hello world.\n" {
-		log.Fatalf("Got body: " + s)
+		log.Fatalf("Got body: %q", s)
 	}
 	return true
 }

sweet/generators/tile38.go

@@ -106,7 +106,7 @@ func (Tile38) Generate(cfg *common.GenConfig) error {
 	if err != nil {
 		log.Printf("=== Server stdout+stderr ===")
 		for _, line := range strings.Split(buf.String(), "\n") {
-			log.Printf(line)
+			log.Print(line)
 		}
 		return fmt.Errorf("error: starting server: %w", err)
 	}
@@ -132,7 +132,7 @@ func (Tile38) Generate(cfg *common.GenConfig) error {
 		if err != nil && buf.Len() != 0 {
 			log.Printf("=== Server stdout+stderr ===")
 			for _, line := range strings.Split(buf.String(), "\n") {
-				log.Printf(line)
+				log.Print(line)
 			}
 		}
 		if err == nil {