cmd/tip: log error when fetching metadata

This error was previously ignored. This caused a silent failure when the
meta URL wasn't accessible.

Change-Id: I4020897ac15fec7b60a46277d81a99a6b6447a7d
Reviewed-on: https://go-review.googlesource.com/45655
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

cmd/tip/tip.go

@@ -315,6 +315,7 @@ var timeoutClient = &http.Client{Timeout: 10 * time.Second}
 func gerritMetaMap() map[string]string {
 	res, err := timeoutClient.Get(metaURL)
 	if err != nil {
+		log.Printf("Error getting Gerrit meta map: %v", err)
 		return nil
 	}
 	defer res.Body.Close()