removed dependency on python-cliff

argparse not used at all
 - docopt used instead

added doc strings to code

using *cmd* prefix in usage strings instead of hardcoding "lmi cmd_name"
in it

updated for changes in current openlmi-tools
do not require python-cliff
removed tracing statements
take "command names" as a valid options

Let's not warn about what seems to be an unhandled command in options
dictionary. Try to pass them to associated function instead.
polished service command

added docstrings and made list interface nicer