LU-9897 utils: remove llverfs dependency on libext2fs

LU-9897 utils: remove llverfs dependency on libext2fs

The llverfs tool can be built with or without libext2fs.

If built without libext2fs then it estimates how many subdirectories
are needed based on the total filesystem size and default settings.
In this case, it calls "chattr" directly to set the "TOPDIR" flag so
directories are still spread across the filesystem, if possible.

Don't unnecessarily seek() the file descriptor if this is not needed.

Improve stats output so it isn't negative if the IO rate changes, and
always print at least _something_ for read and write when run.

Test-Parameters: trivial testlist=conf-sanity
Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Change-Id: Ia1d51ec8d68d3068a9c31e966935149f123ebbe5
Reviewed-on: https://review.whamcloud.com/36016
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>