Managed HVM guests are not displayed by 'xm list' after restarting xend.

This patch prevents writing empty configuration items to the domain's
sexpr configuration file.  Without the empty items, the sexpr is
parsed properly when xend is started.

Signed-off-by: Jim Fehlig <jfehlig@novell.com>

tools/python/xen/xend/XendConfig.py

@@ -730,7 +730,7 @@ class XendConfig(dict):
             
             for key in XENAPI_PLATFORM_CFG:
                 val = sxp.child_value(image_sxp, key, None)
-                if val is not None:
+                if val is not None and val != '':
                     self['platform'][key] = val
             
             notes = sxp.children(image_sxp, 'notes')
@@ -1359,7 +1359,7 @@ class XendConfig(dict):
 
         for key in XENAPI_PLATFORM_CFG:
             val = sxp.child_value(image_sxp, key, None)
-            if val is not None:
+            if val is not None and val != '':
                 self['platform'][key] = val
 
         notes = sxp.children(image_sxp, 'notes')