Fix VNC server after HVM save/restore/migrate, when no vncpasswd specified.

The basic problem was that the "image" section of the sxp had a "None"
in it, which means that on the restore (either on the local machine or
remote machine), the vnc server in the qemu device model literally
needed the string "None" to properly connect.  This simple patch only
puts a vncpasswd entry in the image if it is *not* None in the python
code, thus avoiding the whole issue.

Signed-off-by: Chris Lalancette <clalance@redhat.com>

tools/python/xen/xm/create.py

@@ -725,7 +725,8 @@ def configure_hvm(config_image, vals):
     for a in args:
         if a in vals.__dict__ and vals.__dict__[a] is not None:
             config_image.append([a, vals.__dict__[a]])
-    config_image.append(['vncpasswd', vals.vncpasswd])
+    if vals.vncpasswd is not None:
+        config_image.append(['vncpasswd', vals.vncpasswd])
 
 
 def make_config(vals):