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/init1.go b/test/init1.go
index a888ad7..f6eda6e 100644
--- a/test/init1.go
+++ b/test/init1.go
@@ -33,6 +33,7 @@
 	sys1 := memstats.Sys
 	if sys1-sys > chunk*50 {
 		println("allocated 1000 chunks of", chunk, "and used ", sys1-sys, "memory")
+		panic("init1")
 	}
 }