New module "availability_zones" using context not follow habbit

[Tiantian Gao]

As in nova/availability_zones.py, the method def get_host_availability_zone() expect the first argument "context" is a module rather than a RequestContext object. The code is shown below.
For our preference, argument "context" is better to be a RequestContext object which contains the information of request user.

def get_host_availability_zone(context, host):
 metadata = db.aggregate_metadata_get_by_host(context.get_admin_context(), host, key='availability_zone')
 ....

This style may make coder confuse.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/19900

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/19900
Committed: http://github.com/openstack/nova/commit/6d5e0fd2d488329f66f31a4d6a1153a4a64ed6aa
Submitter: Jenkins
Branch: master

commit 6d5e0fd2d488329f66f31a4d6a1153a4a64ed6aa
Author: gtt116 <[e-mail]>
Date: Thu Jan 17 07:36:43 2013 +0000

    Fix incorrect use of context object

    As in nova/availability_zones.py, the method get_host_availability_zone()
    expects "context" as a module rather than a RequestContext object.
    But for our preference, the argument "context" is better to be a
    RequestContext object. So fix this by passing an context object into the
    method.

    * Fix the usage of argument "context"
    * Add unittest for the module "availability_zones"

    Fix bug lp:#1100598

    Change-Id: I5886ba26131261d97be65f18e9492c40401c5a7f