xm: Use 'vifname' config option to construct a qemu tap name.

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

tools/python/xen/xend/image.py

@@ -873,9 +873,14 @@ class HVMImageHandler(ImageHandler):
             ret.append("-net")
             ret.append("nic,vlan=%d,macaddr=%s,model=%s" %
                        (nics, mac, model))
+            vifname = devinfo.get('vifname')
+            if vifname:
+                vifname = "tap-" + vifname
+            else:
+                vifname = "tap%d.%d" % (self.vm.getDomid(), nics-1)
             ret.append("-net")
-            ret.append("tap,vlan=%d,ifname=tap%d.%d,bridge=%s" %
-                       (nics, self.vm.getDomid(), nics-1, bridge))
+            ret.append("tap,vlan=%d,ifname=%s,bridge=%s" %
+                       (nics, vifname, bridge))
 
         if nics == 0:
             ret.append("-net")