Add a encode() to AnsibleVaultEncryptedUnicode (#19840)

* Add a encode() to AnsibleVaultEncryptedUnicode

Without it, calling encode() on it results in a bytestring
of the encrypted !vault-encrypted string.

ssh connection plugin triggers this if ansible_password
is from a var using !vault-encrypted. That path ends up
calling .encode() instead of using the __str__.

Fixes #19795

* Fix str.encode() errors on py2.6

py2.6 str.encode() does not take keyword arguments.

lib/ansible/parsing/yaml/objects.py

@@ -132,3 +132,6 @@ class AnsibleVaultEncryptedUnicode(yaml.YAMLObject, AnsibleUnicode):
 
     def __unicode__(self):
         return unicode(self.data)
+
+    def encode(self, encoding=None, errors=None):
+        return self.data.encode(encoding, errors)