tests/salt: make sure to use correct dispvm for test

default_dispvm is default management_dispvm, but the test system can
have non-default set, so set both properties.

(cherry picked from commit bef1cbe)

qubes/tests/integ/salt.py

@@ -278,6 +278,7 @@ def setUp(self):
             template_for_dispvms=True, name=dispvm_tpl_name)
         self.loop.run_until_complete(dispvm_tpl.create_on_disk())
         self.app.default_dispvm = dispvm_tpl
+        self.app.management_dispvm = dispvm_tpl
 
     def tearDown(self):
         self.app.default_dispvm = None