libvirt: 'instane' typo while adding configdrive

[Michael Fork]

There was an erroneous reference to 'instane' instead of 'instance' in the code block that builds a libvirt block device for configdrive.

Also, the configdrive block of get_guest_storage_config in nova/virt/libvirt/driver.py has no unit test coverage.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/20058

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/20044
Committed: http://github.com/openstack/nova/commit/9860891a09eb58adadbd519644906e1c6215bf3b
Submitter: Jenkins
Branch: master

commit 9860891a09eb58adadbd519644906e1c6215bf3b
Author: Michael J Fork <email address hidden>
Date: Fri Jan 18 19:03:45 2013 +0000

    libvirt: Fix typo in configdrive implementation

    libvirt configdrive implementation
    references 'instane' instead of 'instance'.
    Also, add a test for adding configdrive block device
    that would catch such an error

    fixes bug 1101352

    Change-Id: I36cba4487ad9d78d4e0366c8c2550603ba155c47