test: ensure all failing tests exit nonzero.

Previously merely printing an error would cause the golden
file comparison (in 'bash run') to fail, but that is no longer
the case with the new run.go driver.

R=iant
CC=golang-dev
https://golang.org/cl/7310087
diff --git a/test/alias1.go b/test/alias1.go
index 4219af8..42cf693 100644
--- a/test/alias1.go
+++ b/test/alias1.go
@@ -17,7 +17,7 @@
 	case uint8:
 		// ok
 	default:
-		println("byte != uint8")
+		panic("byte != uint8")
 	}
 
 	x = uint8(2)
@@ -25,7 +25,7 @@
 	case byte:
 		// ok
 	default:
-		println("uint8 != byte")
+		panic("uint8 != byte")
 	}
 
 	rune32 := false
@@ -37,7 +37,7 @@
 		// must be new code
 		rune32 = true
 	default:
-		println("rune != int and rune != int32")
+		panic("rune != int and rune != int32")
 	}
 
 	if rune32 {
@@ -49,6 +49,6 @@
 	case rune:
 		// ok
 	default:
-		println("int (or int32) != rune")
+		panic("int (or int32) != rune")
 	}
 }