Simplify NVP plugin configuration loading

[Salvatore Orlando]

There are several improvements which could be done on the NVP configuration:
- from a user perspective simplify the way in which a connection to a nvp controller is specified.
Currently we use the following format:
<ip>:<port>:<user>:<pw>:<req_timeout>:<http_timeout>:<retries>:<redirects>
However all these parameters with the exception of the first two are common to all controllers (*)

- from a code perspective, there' a a lot of redundancy in the data structures which handle clusters and controller connections; also there's quite a lot of boilerplate code which could be removed if the common cfg infrastructure is properly leveraged.

* Technically, http_timeout, and redirects could different for each controller.

[Salvatore Orlando (salvatore-orlando)]

Note: This will be important for properly handling multiple controllers in the devstack patch for nvp as we do not have a way in devstack for specifying multi string options.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/21639

[dan wendlandt (danwent)]

this is a pretty big for a bug assigned to rc1. please wrap this up before next week or we will bump to havana.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/26427

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/26427
Committed: http://github.com/openstack/quantum/commit/ea9aeb6de075f391f6a73d6ea2b76d6e452c28bc
Submitter: Jenkins
Branch: master

commit ea9aeb6de075f391f6a73d6ea2b76d6e452c28bc
Author: armando-migliaccio <email address hidden>
Date: Mon Apr 8 17:40:21 2013 -0700

    Simplify NVP plugin configuration

    Fixes bug #1121605

    This patch replacest the nvp_controller_connection configuration option
    with a set of options more intutitive to user which also avoid
    repetitions in ini files.

    In order to simplify the configuration of the plugin, this patch also
    removes named clusters. As the plugin supports a single cluster at
    the moment, this can be simply specified in the [DEFAULT] configuration
    section.

    Also, this patch restrucures nvp_cluster.NvpCluster so that per-cluster
    configuration options are not store anymore multiple times.

    Change-Id: Id5f84220122d7c5f3239e3333cb772247d1ed05e