fix: reporting wrong memory amount for xen host

ccnode/xen.py

 # -*- coding: utf-8 -*-
 
-from libvirtwrapper import LibvirtHypervisor
+from libvirtwrapper import LibvirtHypervisor, MEGABYTE_DIV
 
 
 class XenHypervisor(LibvirtHypervisor):
@@ -30,13 +30,11 @@ class XenHypervisor(LibvirtHypervisor):
     def get_mem(self):
         '''
         '''
-        # real machine memory is the max allocatable size of the Dom0
         mem = None
         try:
-            dom0 = self._lvcon_handle.lookupByID(0)
-            data = dom0.info()[1]
+            data = self._lvcon_handle.getInfo()[1]
             if data:
-                mem = data
+                mem = data * MEGABYTE_DIV
         except:
             pass
         return mem