LU-7544 doc: improve setquota man page

LU-7544 doc: improve setquota man page

Move 'lfs setquota' to a separate man page and change the man page to
use "K, M, G, T, P" suffixes for block limits.

Test-Parameters: trivial
Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: I8de81ebfed86151dbb1ac16690f3b4e377f95366
Reviewed-on: https://review.whamcloud.com/28163
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>