Add tests to testing HVM default features (pae, acpi, apic)
conversion from xm config to libvirt xml. If no pae|acpi|apic
specified in xm config, after conversion, libvirt xml should
by default include:
 <features>
   <pae/>
   <apic/>
   <acpi/>
 </features>
Signed-off-by: NChunyan Liu <cyliu@suse.com>