CBSE-881: improve %complete indicator

Display both batch and msgs stats only under verbose mode

Change-Id: I79a8dfafafd0d84998ecd62affd6e4f0898e8afc
Reviewed-on: http://review.couchbase.org/30814
Reviewed-by: Steve Yen <steve.yen@gmail.com>
Tested-by: Bin Cui <bin.cui@gmail.com>