Increase the rate limiting of GCE's token source. The burst being at 3

means transient errors won't incur such long waits, but repeating
failures shouldn't be retrying every second.

pkg/cloudprovider/gce/token_source.go

@@ -31,7 +31,7 @@ import (
 
 const (
 	// Max QPS to allow through to the token URL.
-	tokenURLQPS = 1
+	tokenURLQPS = .05 // back off to once every 20 seconds when failing
 	// Maximum burst of requests to token URL before limiting.
 	tokenURLBurst = 3
 )