InstanceInfoCache should be availible for deleted instances

[Jason Kölker]

The relationship for instance in the InstanceInfoCache only allows undeleted cache entries. So if you have a reference to a deleted instance, the it will never have that deleted instance's network info, nor will calling out to the network api help ;(.

This breaks usage reporting very badly.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/5067
Committed: http://github.com/openstack/nova/commit/24f4e093b6c7290de06b7aaaa1e4dda96e17e5f9
Submitter: Jenkins
Branch: master

commit 24f4e093b6c7290de06b7aaaa1e4dda96e17e5f9
Author: Trey Morris <email address hidden>
Date: Wed Mar 7 22:22:16 2012 -0600

    info_cache is related to deleted instance

    fixes lp948586

    what is now possible:
    http://pastie.org/3546474

    the problem was there were entities hitting the api to get network data
    for instances that were deleted. Deleted instances did not have the
    backref to info_cache available. The api would then go to network to get
    the info, but since the network structures had already been torn down,
    there was nothing to return. The bug then is that network_info at time
    of instance deletion was expected to be accessible through the
    instance['info_cache'].

    Change-Id: I8ce6ce92e2abe6241d408192ced9526562e978db