[libvirt] Revamped Smbios/Sysinfo support

[Daniel Veillard]

This patch set implements a new way to store system informations and
pass them to the domain, it's modelled on the SMBIOS support in
hypervisors and allow to override those informations in domains:

The simplest is the use of:

  <smbios mode="host"/>

in which case the domain will try to inherit those values from
the Host own values, the classical use case is the use of OEM'ed
Windows versions where one need to export SMBIOS informations from
the host to the guest.
But the <sysinfo> construct allows to define those informations,
for example:

  <sysinfo type="smbios">
    <bios>
      <entry name="vendor">QEmu/KVM</entry>
      <entry name="version">0.13</entry>
    </bios>
    <system>
      <entry name="manufacturer">Fedora</entry>
      <entry name="product">Virt-Manager</entry>
      <entry name="version">0.8.2-3.fc14</entry>
      <entry name="serial">32dfcb37-5af1-552b-357c-be8c3aa38310</entry>
      <entry name="uuid">c7a5fdbd-edaf-9455-926a-d65c16db1809</entry>
    </system>
  </sysinfo>
  <smbios mode="sysinfo"/>

In that case libvirt hypervisor driver will try to set up those values
in the domain emulation.
The patch set attached implement those modes for QEmu, and based on our
previous reviews with Matthias  the first mode should be implementable
in the ESX driver (for just a couple of settings though) and the VirtualBox
driver should be abble to implement both if we understood correctly,

Daniel