Fix libvirt domain XML generation for tap driver

When tap:aio was selected, an empty element was used without being
closed, generating the following error:

UnexpectedError: Problem creating the VM: at line 20: Opening and ending tag mismatch: driver line 17 and disk

control/src/python/workspacecontrol/defaults/lvrt/lvrt_model.py

@@ -165,7 +165,7 @@ def toXML(self):
         if self.driver:
             # file is ignored at the moment
             if self.driver == "tap:aio":
-                x.write(L(3, "<driver name='tap' type='aio'>"))
+                x.write(L(3, "<driver name='tap' type='aio' />"))
 
         x.write(L(3, "<source file='%s' />" % self.source))
         x.write(L(3, "<target dev='%s' />" % self.target))