improve binlog copy management

[svaroqui]

today we have

--backup-binlogs Archive binlogs --backup-binlogs-keep int Number of master binlog to keep (default 10)

Would like to add ( today we only enable client)

--backup-binlogs-method="client|ssh|gomysql|script"
--backup-binlogs-script path to script (parameters: source_ssh_host ,source_ssh_port,source_path, dest_host ,dest_ssh_port, dest_ssh_path ) default empty

[caffeinated92]

options already added in #562 added ssh method for backup binlogs added status for show that master is backing up binlog (previously it will be purged by force-binlog-purge-on-restore)