hvm: enable missing features

Apparently libvirt driver have own defaults for machine features - all
disabled (instead of using libxl defaults). So enable such features
explicitly.

xen-vm-config/vm-template-hvm.xml

@@ -12,6 +12,9 @@
     {disable_network1}<cmdline>-net lwip,client_ip={ip},server_ip={dns2},dns={dns1},gw={gateway},netmask={netmask}</cmdline>{disable_network2}
   </os>
   <features>
+    <pae/>
+    <acpi/>
+    <apic/>
     <viridian/>
   </features>
   <clock offset='variable' adjustment='{timeoffset}' basis='{time_basis}'/>