
##### SUMMARY
This line of code will traceback on Python2 if a vaulted string contains non-ascii characters:

https://github.com/ansible/ansible/blob/devel/lib/ansible/parsing/yaml/objects.py#L131

The function should be defined like this:
``` python
    def __str__(self):
        return to_native(self.data, errors='surrogate_or_strict')
```

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
lib/ansible/parsing/yaml/objects.py

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
Current devel (2.9) and previous versions
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below

```

##### OS / ENVIRONMENT
<!--- Provide all relevant information below, e.g. target OS versions, network device firmware, etc. -->


##### STEPS TO REPRODUCE
I'm not sure if the current ```__str__()``` method ever gets called on Python2.  A quick test by tracing the following playbook shows that ```__unicode__()``` gets called in that playbook.  

```
---
- hosts: localhost
  gather_facts: False
  vars:
    the_secret: !vault |
          $ANSIBLE_VAULT;1.1;AES256
          62666630343233373162323132363462633332356664636165616339303536333334366231303963
          6433666337653864653163623063353932386130646530370a303234633037383966343366343037
          39336433656461656261326165643431633363313562343764373136613338363039366136366439
          6666633836343935660a396336393834326232383636613665316133666464393834623831326562
          6165
  tasks:
  - debug: msg="{{ the_secret }}"
```
(Vault password is 12345)

It probably should be fixed, though, as all it will take to provoke a UnicodeError is some piece of code being changed to do ```'%s' % vault_encrypted_variable_with_non_ascii_chars```.  The %s format string will use ```__str__()``` instead of ```__unicode__()``` and provoke the error.

<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->


##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->

<!--- Paste verbatim command output between quotes -->
```paste below

```

'''
    the base class used to sub-class python built-in objects
    so that we can add attributes to them during yaml parsing
    '''
    _data_source = None
    _line_number = 0
    _column_number = 0
    def _get_ansible_position(self):
        return (self._data_source, self._line_number, self._column_number)
    def _set_ansible_position(self, obj):
        try:
            (src, line, col) = obj
        except (TypeError, ValueError):
            raise AssertionError(
                'ansible_pos can only be set with a tuple/list '
                'of three values: source, line number, column number'
            )
        self._data_source = src
        self._line_number = line
        self._column_number = col
    ansible_pos = property(_get_ansible_position, _set_ansible_position)
class AnsibleMapping(AnsibleBaseYAMLObject, dict):
    ''' sub class for dictionaries '''
    pass
class AnsibleUnicode(AnsibleBaseYAMLObject, text_type):