Namechange events_processed -> event_processing_finished

from PR review, also adding tests to assert that the
value is passed from the stdout_handle to the UnifiedJob
object on finalization of job run in tasks.py

awx/main/models/unified_jobs.py

@@ -924,7 +924,7 @@ class UnifiedJob(PolymorphicModel, PasswordFieldsModel, CommonModelNameNotUnique
         return self.event_class.objects.filter(**{self.event_parent_key: self.id})
 
     @property
-    def events_processed(self):
+    def event_processing_finished(self):
         '''
         Returns True / False, whether all events from job have been saved
         '''