add ignore_errors to fix keyword arg warning (#15668)

When running an ad hoc command with --tree that fails a keyword argument error is produced.

```shell
ansible-server$ ansible server1 -a "/bin/false" -t temp
server1 | FAILED | rc=1 >>


 [WARNING]: Failure when attempting to use callback plugin (</Library/Python/2.7/site-packages/ansible/plugins/callback/tree.CallbackModule object at 0x10f6f1dd0>): v2_runner_on_failed() got an unexpected keyword argument 'ignore_errors'
```
Seems that the `v2_runner_on_failed()` call is missing "ignore_errors=False" parameter.  Without this fix --tree will not work when ad hoc commands fail.

lib/ansible/plugins/callback/tree.py

@@ -63,7 +63,7 @@ class CallbackModule(CallbackBase):
     def v2_runner_on_ok(self, result):
         self.result_to_tree(result)
 
-    def v2_runner_on_failed(self, result):
+    def v2_runner_on_failed(self, result, ignore_errors=False):
         self.result_to_tree(result)
 
     def v2_runner_on_unreachable(self, result):