cloner: Clear domain <title> as well

Otherwise in virt-manager the two VMs will be identical

https://bugzilla.redhat.com/show_bug.cgi?id=1687334

Signed-off-by: Cole Robinson <crobinso@redhat.com>

tests/data/clone/general-cfg-in.xml

@@ -3,6 +3,7 @@
   <uuid>aaa3ae22-fed2-bfbd-ac02-3bea3bcfad82</uuid>
   <memory>262144</memory>
   <currentMemory>262144</currentMemory>
+  <title>footitle</title>
   <vcpu>1</vcpu>
   <os>
     <type arch='i686' machine='pc'>hvm</type>

virtinst/cloner.py

@@ -410,6 +410,8 @@ class Cloner(object):
 
         self._guest.name = self._clone_name
         self._guest.uuid = self._clone_uuid
+        self._guest.title = None
+
         self._clone_macs.reverse()
         for dev in self._guest.devices.graphics:
             if dev.port and dev.port != -1: