cmd: Tidy up -help output

cmd: Tidy up -help output

Tidy up the output that comes from cmd's -help option by wrapping
at 78 characters, and picking the breaks sensibly. This changes:

Usage: ./vos move -id <volume name or ID> -fromserver <machine name on source> -
frompartition <partition name on source> -toserver <machine name on destination>
 -topartition <partition name on destination> [-live] [-cell <cell name>] [-noau
th] [-localauth] [-verbose] [-encrypt] [-noresolve] [-help]

to...

Usage: ./vos move -id <volume name or ID>
         -fromserver <machine name on source>
         -frompartition <partition name on source>
         -toserver <machine name on destination>
         -topartition <partition name on destination> [-live]
         [-cell <cell name>] [-noauth] [-localauth] [-verbose]
         [-encrypt] [-noresolve] [-help]

Change-Id: I494c287a9370d052763b464df33e69a936edef71
Reviewed-on: http://gerrit.openafs.org/4546
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>