LU-18564 doc: difference between lfs 'osts' and 'check ost'

LU-18564 doc: difference between lfs 'osts' and 'check ost'

Update man page for lfs.1 to record commands behave
differently. 'check ost' will perform RPC, 'osts' will not.

Test-Parameters: trivial
Signed-off-by: Richard Henwood <rhenwood@ddn.com>
Change-Id: If7faf0d0108fad2f79486ca1a768a23c99b1dfb3
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57468
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Mathieu Dube <mdube@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>