[FAB-16056] Display config block num for CLI

CLI user want to see only the config block num, instead of two block
numbers when fetching the config block.

However the newest block number log can not be removed. So add a new
log to point out the config block number:

$ peer channel fetch config -c mychannel

InitCmdFactory -> INFO 001 Endorser and orderer connections initialized
readBlock -> INFO 002 Received block: 4
fetch -> INFO 003 Retrieving last config block: 2
readBlock -> INFO 004 Received block: 2

Signed-off-by: Shitaibin <hz_stb@163.com>
Change-Id: I1d359b93f4d48786b8404cbb3484f0710c7eb829

peer/channel/fetch.go

@@ -80,6 +80,7 @@ func fetch(cmd *cobra.Command, args []string, cf *ChannelCmdFactory) error {
 			return err2
 		}
 		block, err = cf.DeliverClient.GetSpecifiedBlock(lc)
+		logger.Infof("Retrieving last config block: %d", lc)
 	default:
 		num, err2 := strconv.Atoi(args[0])
 		if err2 != nil {