etcdctl: update -peers to default to use schema

Change its default value from `127.0.0.1:4001,127.0.0.1:2379` to
`http://127.0.0.1:4001,http://127.0.0.1:2379`

Adding HTTP schema makes its format consistent with etcd's xxx-urls
flags.

etcdctl/command/util.go

@@ -69,7 +69,7 @@ func getPeersFlagValue(c *cli.Context) []string {
 
 	// If we still don't have peers, use a default
 	if peerstr == "" {
-		peerstr = "127.0.0.1:4001,127.0.0.1:2379"
+		peerstr = "http://127.0.0.1:4001,http://127.0.0.1:2379"
 	}
 
 	return strings.Split(peerstr, ",")