Fix memory leak in xend

I found that xend's memory usage grows considerably when running a
script such as

while true; do xm new foo ; sleep 2s; xm delete foo ; sleep 2s; done

XendAPIStore maintains a list of class instances and in the case of
new/create operation, an associated VMMetrics object is stashed in the
list but never removed on delete/shutdown.  This patch removes the
instance by invoking XendBase.destroy() method.

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

tools/python/xen/xend/XendDomain.py

@@ -1088,6 +1088,7 @@ class XendDomain:
         log.info("Domain %s (%s) deleted." %
                  (dominfo.getName(), dominfo.info.get('uuid')))
                 
+        dominfo.metrics.destroy()
         self._managed_domain_unregister(dominfo)
         self._remove_domain(dominfo)
         XendDevices.destroy_device_state(dominfo)