Switches bug fix and tweaks added

• backup_folder switch added, previously availably only through module load
• dd_buffer and lv_size added for tweaking. In case your backup slows down and lv snapshot gets overrun, change the lv_size to something bigger (never happened to us). dd_buffer is for in memory buffering, useful if remote hardware is slow, but local is fast. Loads in memory and sends data remotely to unload as fast as it can. 128M is suitable for 1gbit/s, but if you have lots of spare ram on nodes and backup server you can increase this.