Libra worker should support node weights

[David Shrewsbury]

Need to handle node weighting. We would map the value from the API server request to the HAProxy equivalent config value.

See the 'weight' option to the 'server' config value in HAProxy docs:

  http://cbonte.github.com/haproxy-dconv/configuration-1.4.html#5-weight

From the Atlas-LB API docs:

---
The caller can assign the relevant weights to nodes using the weight attribute of the node element.

The weight of a node determines the portion of requests or connections it services compared to the other nodes of the load balancer. For example, if node A has a weight of 2 and node B has a weight of 1, then the loadbalancer will forward twice as many requests to node A than to node B. If the weight attribute is not specified, then the node's weight is implicitly set to "1".
---

Example:

{
  "nodes": [
             {
               "address": "10.1.1.1",
               "port": "80"
             },
             {
               "address": "10.2.2.1",
               "port": "80",
               "weight": "2"
             },
             {
               "address": "10.2.2.2",
               "port": "88",
               "condition": "DISABLED",
               "weight": "2"
             }
           ]
}

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/21330

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/21330
Committed: http://github.com/stackforge/libra/commit/53fedfca2a3167341a1839be128a29bdec3b50a0
Submitter: Jenkins
Branch: master

commit 53fedfca2a3167341a1839be128a29bdec3b50a0
Author: David Shrewsbury <email address hidden>
Date: Wed Feb 6 11:00:20 2013 -0500

    Support server node weights.

    Support setting a weighting value for each node that will determine
    the proportion of load balancing requests that it receives in relation
    to the other defined servers and their weights.

    Also adds a file describing the worker JSON message versioning.

    Fixes bug 1117349

    Change-Id: Ie1460c165f03b0523ee28d864b74ea9e5858b256