engine: With --test-first-run, don't try default URI detection

default URI detection gets testing via the 'connect' dialog, this
makes it easier to test the fallback when no packages are locally
present

virtManager/engine.py

@@ -233,9 +233,10 @@ class vmmEngine(vmmGObject):
         except Exception:
             logging.exception("Error talking to PackageKit")
 
+        tryuri = None
         if ret:
             tryuri = "qemu:///system"
-        else:
+        elif not self.config.test_first_run:
             tryuri = vmmConnect.default_uri()
 
         if tryuri is None: