Implement vault encrypted yaml variables. (#16274)

Make !vault-encrypted create a AnsibleVaultUnicode
yaml object that can be used as a regular string object.

This allows a playbook to include a encrypted vault
blob for the value of a yaml variable. A 'secret_password'
variable can have it's value encrypted instead of having
to vault encrypt an entire vars file.

Add __ENCRYPTED__ to the vault yaml types so
template.Template can treat it similar
to __UNSAFE__ flags.

vault.VaultLib api changes:
    - Split VaultLib.encrypt to encrypt and encrypt_bytestring

    - VaultLib.encrypt() previously accepted the plaintext data
      as either a byte string or a unicode string.
      Doing the right thing based on the input type would fail
      on py3 if given a arg of type 'bytes'. To simplify the
      API, vaultlib.encrypt() now assumes input plaintext is a
      py2 unicode or py3 str. It will encode to utf-8 then call
      the new encrypt_bytestring(). The new methods are less
      ambiguous.

    - moved VaultLib.is_encrypted logic to vault module scope
      and split to is_encrypted() and is_encrypted_file().

Add a test/unit/mock/yaml_helper.py
It has some helpers for testing parsing/yaml

Integration tests added as roles test_vault and test_vault_embedded

test/units/parsing/yaml/test_dumper.py

@@ -0,0 +1,64 @@
+# coding: utf-8
+# This file is part of Ansible
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+
+# Make coding more python3-ish
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+import io
+import yaml
+
+try:
+    from _yaml import ParserError
+except ImportError:
+    from yaml.parser import ParserError
+
+from ansible.parsing.yaml import dumper
+from ansible.parsing.yaml.loader import AnsibleLoader
+
+from ansible.compat.tests import unittest
+from ansible.parsing.yaml import objects
+from ansible.parsing import vault
+
+from units.mock.yaml_helper import YamlTestUtils
+
+class TestAnsibleDumper(unittest.TestCase, YamlTestUtils):
+    def setUp(self):
+        self.vault_password = "hunter42"
+        self.good_vault = vault.VaultLib(self.vault_password)
+        self.vault = self.good_vault
+        self.stream = self._build_stream()
+        self.dumper = dumper.AnsibleDumper
+
+    def _build_stream(self,yaml_text=None):
+        text = yaml_text or u''
+        stream = io.StringIO(text)
+        return stream
+
+    def _loader(self, stream):
+        return AnsibleLoader(stream, vault_password=self.vault_password)
+
+    def test(self):
+        plaintext = 'This is a string we are going to encrypt.'
+        avu = objects.AnsibleVaultEncryptedUnicode.from_plaintext(plaintext, vault=self.vault)
+
+        yaml_out = self._dump_string(avu, dumper=self.dumper)
+        stream = self._build_stream(yaml_out)
+        loader = self._loader(stream)
+
+        data_from_yaml = loader.get_single_data()
+
+        self.assertEquals(plaintext, data_from_yaml.data)