[backend] Better identify when user processes are killed and provide an...

[backend] Better identify when user processes are killed and provide an explanation to the user in these cases

beat/web/backend/models.py

@@ -1296,6 +1296,11 @@ class JobSplit(models.Model):
                         else:
                             self.status = Job.COMPLETED if \
                                 result.status == 0 else Job.FAILED
+                            if result.status in (-15, 15, -9, 9):
+                                # job received a term/kill signal
+                                if not result.usrerr:
+                                    result.usrerr = 'User process was ' \
+                                        'terminated by an external agent'
                             if result.id is None: result.save()
                             self.result = result