Swap not being cleaned up on exception

[Rick Harris]

If an exception is raised during spawn instance (in XenServer), we can end up leaving the swap as an orphaned VDI.

There are two approaches to fixing this:

1. A long, involved approach of refactoring much of _create_vm into separate, atomic steps that can support fine-grained undoability.

2. Making _create_vm's undo func call _destroy instead of _destroy_vm.

1) is probably too risky for this late in the release, so I'm opting for 2) with an eye to tackling a more complete rework down the road.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/4836

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/4836
Committed: http://github.com/openstack/nova/commit/f0a172ea8bcd5b241115210fcdbe33cf268ef051
Submitter: Jenkins
Branch: master

commit f0a172ea8bcd5b241115210fcdbe33cf268ef051
Author: Rick Harris <email address hidden>
Date: Fri Mar 2 22:26:20 2012 +0000

    Cleanup swap in _create_vm undo

    Fixes bug 945198

    Change-Id: I697fab1bbfdd45fc22d5490524e138c4f377bc58