cgget: unify -h|--help output

cgget: unify -h|--help output

this patch unify -h|--help output.
old version:
$ cgget -h
Usage: cgget [-nv] [-r<name>] [-g<controller>] [-a] <path> ...
   or: cgget [-nv] [-r<name>] -g<controller>:<path> ...

new version:
$ cgget -h
Usage: cgget [-nv] [-r <name>] [-g <controller>] [-a] <path> ...
   or: cgget [-nv] [-r <name>] -g <controller>:<path> ...
Print parameter(s) of given group(s).
  -a, --all					Print info about all relevant controllers
  -g <controller>			Controller which info should be displaied
  -g <controller>:<path>	Control group whih info should be displaied
  -h, --help				Display this help
  -n						Do not print headers
  -r, --variable <name>		Define parameter to display
  -v, --values-only			Print only values, not parameter names

Signed-off-by: Ivana Hutarova Varekova <varekova@redhat.com>
Signed-off-by: Jan Safranek <jsafrane@redhat.com>