LU-16974 utils: make bandwidth options consistent

LU-16974 utils: make bandwidth options consistent

The "lfs mirror extend|resync" and "lfs migrate" commands all have
the ability to limit IO bandwidth. Some used "--bandwidth" and
others used "--bandwidth-limit". Make them all the same.

They accept the longer "--bandwidth-limit" for compatibility, but
only "--bandwidth" will be documented for brevity and ease of use.
The getopt_long() options can be abbreviated to any unique prefix,
so both do not need to be specified.

Update the usage messages and man pages to reflect these options.
Minor nearby code style fixes to the man pages as well.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ie8702bedba9fbfa5b0ea473853a7b5480e61abb5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/59411
Tested-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>