add extension name to command help doc

[yong sheng gong]

After neutron client supports extension, we had better indicate the command extension source.
for example:
$ neutron -h
....
  fox-sockets-create [fox_sockets]
  fox-sockets-delete [fox_sockets]
  fox-sockets-list [fox_sockets] Socket extsion list command.
  fox-sockets-show [fox_sockets]
  fox-sockets-update [fox_sockets]
...

$ neutron help fox-sockets-list
usage: neutron fox-sockets-list [-h] [-f {csv,html,json,table,value,yaml}]
                                [-c COLUMN] [--max-width <integer>]
                                [--quote {all,minimal,none,nonnumeric}]
                                [--request-format {json,xml}] [-D] [-F FIELD]
                                [-P SIZE] [--sort-key FIELD]
                                [--sort-dir {asc,desc}]

[fox_sockets] List fox sockets.
......

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/214961

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/214961
Committed: https://git.openstack.org/cgit/openstack/python-neutronclient/commit/?id=45ed3ecd30a455578662408f14270922cda38b76
Submitter: Jenkins
Branch: master

commit 45ed3ecd30a455578662408f14270922cda38b76
Author: gong yong sheng <[e-mail]>
Date: Thu Aug 20 13:52:50 2015 +0800

    Add extension name to extension's command help text line

    Currently, the cliff does not support to group commands. A good
    way to differentiate the commands from extension modules is to
    prefix the commands with extension name.

    Change-Id: Ib16404c6098340ca90e9548134d4115f5abbf5f6
    Closes-Bug:#1486829