SCM inventory cancel propagation

For manually initiated inventory updates, also cancel the source
project of "sync" type, like jobs do

For automatic inventory updates spawned from source project update,
of launch type "scm", handle contigency cases

awx/main/tasks.py

@@ -1391,6 +1391,15 @@ class RunProjectUpdate(BaseTask):
             except Exception as e:
                 # A failed file update does not block other actions
                 logger.error('Encountered error updating project dependent inventory: {}'.format(e))
+
+            # Stop all dependent inventory updates if project update was canceled
+            project_update.refresh_from_db()
+            if project_update.cancel_flag:
+                break
+            # Don't update inventory scm_revision if update was canceled
+            local_inv_update.refresh_from_db()
+            if local_inv_update.cancel_flag:
+                continue
             inv_src.scm_last_revision = scm_revision
             inv_src.save(update_fields=['scm_last_revision'])