livirt+xen: failed to snapshot a paused instance

[Anthony PERARD]

tempest.api.compute.images.test_images.ImagesTestJSON.test_create_image_from_paused_server fail on the XenProject CI loop.

For example in this run: http://logs.openstack.xenproject.org/49/447449/1/silent/dsvm-tempest-xen/bb39806/

Traceback (most recent call last):
  File "tempest/api/compute/images/test_images.py", line 83, in test_create_image_from_paused_server
    wait_for_server=False)
  File "tempest/api/compute/base.py", line 326, in create_image_from_server
    image_id=image_id)
tempest.exceptions.SnapshotNotFoundException: Server snapshot image c2754ccf-6a8f-4d73-a942-25fef8c99e35 not found.

In n-cpu.log:
libvirtError: Requested operation is not valid: Domain '30' has to be running because libxenlight will suspend it

Environment
===========
The XenProject CI loop:
Ubuntu 16.04
libvirt version: 1.3.1, package: 1ubuntu10.8