btrfs-progs: stat info for btrfs rescue chunk-recover

btrfs-progs: stat info for btrfs rescue chunk-recover

chunk-recover need to use many many time in scan_devices(),
and no output in screen:
 # btrfs rescue chunk-recover /dev/sda6
 (no output here, but need long time)

To notice user that "the command is not hang", this patch add
dynamic updated stat information in above period:
 # btrfs rescue chunk-recover /dev/sda6
 Scanning: DONE in dev[0], 19998441472 in dev[1], DONE in dev[2]
 (until)
 Scanning: DONE in dev0, DONE in dev1, DONE in dev2
 Check chunks successfully with no orphans
 Recover the chunk tree successfully.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>