Fix error when guest's primary_address is not set

Fixes the following error:
    'ResultGuestData' object has no attribute 'primary_address'

tmt/steps/report/reportportal.py

@@ -526,7 +526,7 @@ def go(self, *, logger: Optional[tmt.log.Logger] = None) -> None:
                     test_name = result.name
                     test_time = result.start_time or self.time()
                     # for guests, save their primary address
-                    if result.guest.primary_address:
+                    if getattr(result.guest, 'primary_address', None):
                         item_attributes.append({
                             'key': 'guest_primary_address',
                             'value': result.guest.primary_address})