vdsm: Create VMs for the POWER architecture

This includes changes necessary to create VMs in the POWER architecture
 and run ppc64 guests in x86-64 hosts. These changes are:

- Allow the architecture of a guest to be different from the host,
  in order to allow x86-64 hosts to test ppc64 specific code
- Execute x86 specific QEMU features only in x86-64 guests, like
SMBIOS, guest cpu flags and processor models, ACPI
- Create a virtual USB keyboard in ppc64 guests (this is not done
  automatically like in the x86-64)
- Create a virtual USB mouse in ppc64 guests
- Use the Standard VGA device instead of the Cirrus Logic VGA in ppc64
  guests
- Change the default drive interface to SCSI in ppc64 guests
- Increase the default memory size for fake ppc64 KVM guests
- Tests covering the PPC64 specific code

Change-Id: Iba5026f254d8212f522836f856c2027c04b1d247
Signed-off-by: Vitor de Lima <vitor.lima@eldorado.org.br>
Signed-off-by: Leonardo Bianconi <leonardo.bianconi@eldorado.org.br>
Reviewed-on: http://gerrit.ovirt.org/18718
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Michal Skrivanek <michal.skrivanek@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>