[Merge] ~paelzer/ubuntu/+source/nova:fix-libvirt-dependency into ~ubuntu-server-dev/ubuntu/+source/nova:master

[ChristianEhrhardt]

I wanted to test build but the current in flight 2:16.0.0~b1-0ubuntu5 fails as-is (e.g. build depends on python-pypowervm).
I assume you are resolving those anyway as time permits - so I'll have to wait for your to review and hopefully shove this change into 2:16.0.0~b1-0ubuntu5 as well.
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https://code.launchpad.net/~paelzer/ubuntu/+source/nova/+git/nova/+merge/324778
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