LU-10705 utils: add "lfs find --blocks"

LU-10705 utils: add "lfs find --blocks"

Add support for "lfs find --blocks|-b <block>" to be able to find
files with the specified number of allocated blocks (in kilobytes or
other specified units). This is distinct from "--size <size>" since
that doesn't properly check the space used for sparse files.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I7d48f919d95242c11ef7d3075ecc3f7e963ebbe5
Reviewed-on: https://review.whamcloud.com/31393
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>