Python 3: fix AnsibleError formatting

If you convert the error string to bytes and embed it inside another
error string, you get

  Prefix:

  b'Embedded\nerror\nstring'

which is not what we want.

But we also don't want Unicode in error messages causing unexpected
UnicodeEncodeErrors when on Python 2.

So let's convert the error message into the native string type (bytes on
Python 2, unicode on Python 3).

lib/ansible/errors/__init__.py

@@ -19,11 +19,18 @@
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
-import os
-
 from ansible.errors.yaml_strings import *
 from ansible.utils.unicode import to_unicode, to_bytes
 
+
+if str is bytes:
+    # Python 2
+    to_str = to_bytes
+else:
+    # Python 3
+    to_str = to_unicode
+
+
 class AnsibleError(Exception):
     '''
     This is the base class for all errors raised from Ansible code,
@@ -49,7 +56,7 @@ class AnsibleError(Exception):
         if obj and isinstance(obj, AnsibleBaseYAMLObject):
             extended_error = self._get_extended_error()
             if extended_error:
-                self.message = 'ERROR! %s\n\n%s' % (message, to_bytes(extended_error))
+                self.message = 'ERROR! %s\n\n%s' % (message, to_str(extended_error))
         else:
             self.message = 'ERROR! %s' % message