Make sure the admin_mode prop register only once

[Jeffrey Zhang]

If we register it twice, the `<zaqar>/tools/config/generate_sample.sh` script will generate two `admin_mode` in the config file.

After registered in cli by using `register_cli_opt`, the prop can be configured through configure file. There is no need to register again by using `register_opt` method.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Jeffrey Zhang (<email address hidden>) on branch: master
Review: https://review.openstack.org/123961

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/135012

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/135012
Committed: https://git.openstack.org/cgit/openstack/zaqar/commit/?id=ab74a88503a6a6420f3d4877a3edf7a340660106
Submitter: Jenkins
Branch: master

commit ab74a88503a6a6420f3d4877a3edf7a340660106
Author: Flavio Percoco <email address hidden>
Date: Mon Nov 17 17:56:23 2014 +0100

    Update oslo-config-generation code

    Oslo's config generator has been moved under oslo.config, which doesn't
    require using a bash script anymore.

    The patch removes the old scripts and updates the generation task in
    tox.ini

    Closes-bug: #1373800

    Change-Id: Ia757b0d141f8557144108d386496d1e9bfc7333f