Add support for arm64 images

This patch enables proper support for arm64 images by disabling VNC support
and adding several properties to the image in glance that are necessary to
boot correctly:
  hw_cdrom_bus=virtio
  hw_machine_type=virt
  os_command_line='console=ttyAMA0'

Change-Id: I68c9a5e0e083af2f92875c3bdf70df750f6e4d8f
diff --git a/lib/nova_plugins/hypervisor-libvirt b/lib/nova_plugins/hypervisor-libvirt
index 4d1eb6c..a6a87f9 100644
--- a/lib/nova_plugins/hypervisor-libvirt
+++ b/lib/nova_plugins/hypervisor-libvirt
@@ -54,6 +54,12 @@
         iniset $NOVA_CONF DEFAULT vnc_enabled "false"
     fi
 
+    # arm64-specific configuration
+    if is_arch "aarch64"; then
+        # arm64 architecture currently does not support graphical consoles.
+        iniset $NOVA_CONF DEFAULT vnc_enabled "false"
+    fi
+
     ENABLE_FILE_INJECTION=$(trueorfalse False ENABLE_FILE_INJECTION)
     if [[ "$ENABLE_FILE_INJECTION" = "True" ]] ; then
         # When libguestfs is available for file injection, enable using