veyron,veyron2: rename runtime.Shutdown to runtime.Cleanup.

Context:
https://docs.google.com/a/google.com/document/d/1Sfq1ZEEPtxMFR2Wj6SFNMlNNXZ9xnuz-Cep73RXmBwI/edit

Change-Id: I20b89e7acf70f97c3216bc155e7afcce0cc5db0a
diff --git a/tools/mounttable/main.go b/tools/mounttable/main.go
index a59a17b..61a93d6 100644
--- a/tools/mounttable/main.go
+++ b/tools/mounttable/main.go
@@ -7,6 +7,6 @@
 )
 
 func main() {
-	defer rt.Init().Shutdown()
+	defer rt.Init().Cleanup()
 	impl.Root().Main()
 }