sheep: reduce auto recovery log

Currently, auto recovery process produces one log message per one object.
The log messages consume too large disk space when a cluster has many
objects. This patch reduces the disk consumption by printing progress in a
style of percentage. The existing message is logged in debug level.

Signed-off-by: Saeki Masaki <saeki.masaki@po.ntts.co.jp>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>