Don't change list to tuple when get info from libvirt

[Shuangtai Tian]

In the libvirt.driver, we now use the code like this:
(state, _max_mem, _mem, _cpus, _t) = virt_dom.info()

if the libvirt add new variables in the domain info, the code will be failed.
the error will like this :
 File "/opt/stack/nova/nova/service.py", line 180, in start
    self.manager.init_host()
  File "/opt/stack/nova/nova/compute/manager.py", line 974, in init_host
    self._init_instance(context, instance)
  File "/opt/stack/nova/nova/compute/manager.py", line 882, in _init_instance
    drv_state = self._get_power_state(context, instance)
  File "/opt/stack/nova/nova/compute/manager.py", line 990, in _get_power_state
    return self.driver.get_info(instance)["state"]
  File "/opt/stack/nova/nova/virt/libvirt/driver.py", line 3462, in get_info
    (state, max_mem, mem, num_cpu, cpu_time) = virt_dom.info()
ValueError: too many values to unpack

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/80184

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/80192

[Sean Dague (sdague)]

This requires upstream (unreleased) libvirt to trigger, so setting to medium

[Daniel Berrange (berrange)]

I don't believe there is any bug here. Libvirt will *never* add new fields to existing C structs, since that would break ABI compatibility, so by implication the getInfo() list will not get extra elements.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/80184
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=8fa190c0d4ede0acc8ed4a462a5ebb751380143c
Submitter: Jenkins
Branch: master

commit 8fa190c0d4ede0acc8ed4a462a5ebb751380143c
Author: Shuangtai Tian <email address hidden>
Date: Thu Mar 13 14:13:54 2014 +0800

    Use the list when get information from libvirt

    If the libvirt adds new elements to the domain info struct or others,
    when use the new libvirt, there will be a valueError (too many values
    to unpack). When we get information from libvirt, we should use the
    original variable format. This change is for compatibility with upcoming
    versions of libvirt which change this signature.

    Change-Id: I0271a260a53fe8f5fc17b2934ebe3a3c9ee0c130
    Closes-Bug: #1291805

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/80192
Committed: https://git.openstack.org/cgit/openstack/ceilometer/commit/?id=0b3fa781b82246b5410f5e3520c0d9e50ef2bc1f
Submitter: Jenkins
Branch: master

commit 0b3fa781b82246b5410f5e3520c0d9e50ef2bc1f
Author: Shuangtai Tian <email address hidden>
Date: Thu Mar 13 14:30:14 2014 +0800

    Use the list when get information from libvirt

    If the libvirt adds new elements to the domain info struct or others,
    when use the new libvirt, there will be a valueError (too many values
    to unpack). When we get information from libvirt, we should use the
    original variable format. This change is for compatibility with upcoming
    versions of libvirt which change this signature.

    Change-Id: I885a48b730acd618e7cefc93cee3d69226575b7c
    Closes-Bug: #1291805