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

[ChristianEhrhardt]

Well since you backport to Xenial you might want to keep it, but we should remember to drop on 18.04 if that is your issue accepting this.
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https://code.launchpad.net/~paelzer/ubuntu/+source/nova/+git/nova/+merge/324778
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