[IMP] runbot: keep result on kill if result is failure

When a build is killed, result will be set to manually killed,
removing the 'error' or 'warn' result.

This commit removes this behaviour in order to keep error result
in this case.

runbot/models/build.py

@@ -535,7 +535,10 @@ class runbot_build(models.Model):
             self.env.cr.commit()  # commit between each build to minimise transactionnal errors due to state computations
             self.invalidate_cache()
             if build.requested_action == 'deathrow':
-                build._kill(result='manually_killed')
+                result = None
+                if build.local_state != 'running' and build.global_result not in ('warn', 'ko'):
+                    result = 'manually_killed'
+                build._kill(result=result)
                 continue
 
             if build.requested_action == 'wake_up':