nova-compute requires root /w connection_type=xenapi

[Dan Prince]

Using 2011.2~bzr971.

When running nova-compute with connection_type=xenapi I get the following exception when when nova-compute tries to stream data to the VBD:

(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/compute/manager.py", line 234, in run_instance
(nova.compute.manager): TRACE: self.driver.spawn(instance_ref)
(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/virt/xenapi_conn.py", line 188, in spawn
(nova.compute.manager): TRACE: self._vmops.spawn(instance)
(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/virt/xenapi/vmops.py", line 117, in spawn
(nova.compute.manager): TRACE: vdi_uuid = self._create_disk(instance)
(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/virt/xenapi/vmops.py", line 113, in _create_disk
(nova.compute.manager): TRACE: instance.image_id, user, project, disk_image_type)
(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/virt/xenapi/vm_utils.py", line 386, in fetch_image
(nova.compute.manager): TRACE: access, image_type)
(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/virt/xenapi/vm_utils.py", line 541, in _fetch_image_glance
(nova.compute.manager): TRACE: session, instance_id, image, access, image_type)
(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/virt/xenapi/vm_utils.py", line 456, in _fetch_image_glance_disk
(nova.compute.manager): TRACE: lambda dev:
(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/virt/xenapi/vm_utils.py", line 944, in with_vdi_attached_here
(nova.compute.manager): TRACE: return f(dev)
(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/virt/xenapi/vm_utils.py", line 458, in <lambda>
(nova.compute.manager): TRACE: virtual_size, image_file))
(nova.compute.manager): TRACE: File "/usr/lib/pymodules/python2.6/nova/virt/xenapi/vm_utils.py", line 1017, in _stream_disk
(nova.compute.manager): TRACE: with open('/dev/%s' % dev, 'wb') as f:
(nova.compute.manager): TRACE: IOError: [Errno 13] Permission denied: '/dev/sdb'
(nova.compute.manager): TRACE:

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Couple of ways to go about fixing this. Adding a 'sudo chown' to give nova permission to write to the device seems like the simplest way ((especially since nova already has sudo privs). We could also mess with /etc/udev/ and have the devices show up to a special group that the nova user belongs to and thus has write access. Given that we remap the devices for Maverick support already the sudo looks more appealing for now.