LU-297 improve llverfs to display the current read/write performance

This patch changes show_filename() to show_rate() in llverfs.c to
display the current read/write file name and performance, along with
an estimate of how long the whole read/write operation will continue.

The patch also changes "fast" to "partial" and fixes some typos in
the comments of llverdev.c and llverfs.c.

Signed-off-by: Yu Jian <yujian@whamcloud.com>
Change-Id: I94cb112ae9a38b1128e53021aa0c1f1e8e5411af
Reviewed-on: http://review.whamcloud.com/1110
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>