Adding the missing HostDomain config option

The ``HostDomain`` config type have been added few months ago [1]
however the config option have been forgotten and this new type
isn't importable.

When we try to import this type without defining a new related cfg
option we get the following issue:

```
AttributeError: module 'oslo_config.cfg' has no attribute 'HostDomain'
```

These changes allow us to import this new type and allow us to use
it in our configs:

```
>>> from oslo_config import cfg
>>> foo = cfg.HostDomain('foo')
>>> foo.type.__call__("1")
...
During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "~/oslo.config/oslo_config/types.py", line 893, in __call__
     raise ValueError(
ValueError: 1 is not a valid host address
>>> foo.type.__call__("host_name")
'host_name'
```

Also properly initialize HostDomain because The HostDomain class wasn't
calling super in it's __init__() method, which resulted in the type_name not
being set properly for instances of that class.

[1] 6480356928

Change-Id: Ie947803f61ba0ef080018e0447de894a400d7975
Closes-Bug: 1924283

oslo_config/cfg.py

@@ -1175,6 +1175,28 @@ class HostAddressOpt(Opt):
                                              **kwargs)
 
 
+class HostDomainOpt(Opt):
+
+    r"""Option for either an IP or a hostname.
+
+    Like HostAddress with the support of _ character.
+
+    Option with ``type`` :class:`oslo_config.types.HostDomain`
+
+    :param name: the option's name
+    :param version: one of either ``4``, ``6``, or ``None`` to specify
+       either version.
+    :param \*\*kwargs: arbitrary keyword arguments passed to :class:`Opt`
+
+    .. versionadded:: 8.6
+    """
+
+    def __init__(self, name, version=None, **kwargs):
+        super(HostDomainOpt, self).__init__(name,
+                                            type=types.HostDomain(version),
+                                            **kwargs)
+
+
 class URIOpt(Opt):
 
     r"""Opt with URI type

oslo_config/tests/test_generator.py

@@ -1872,5 +1872,32 @@ class HostAddressTestCase(base.BaseTestCase):
         self.assertEqual(expected, result)
 
 
+class HostDomainTestCase(base.BaseTestCase):
+
+    opts = [cfg.HostDomainOpt('foo', help='foo option', default='0.0.0.0')]
+
+    def test_host_domain(self):
+
+        config = [("namespace", [("alpha", self.opts)])]
+        groups = generator._get_groups(config)
+
+        out = io.StringIO()
+        formatter = build_formatter(out)
+        generator._output_opts(formatter, 'alpha', groups.pop('alpha'))
+        result = out.getvalue()
+
+        expected = textwrap.dedent('''
+        [alpha]
+
+        #
+        # From namespace
+        #
+
+        # foo option (host domain value)
+        #foo = 0.0.0.0
+        ''').lstrip()
+        self.assertEqual(expected, result)
+
+
 GeneratorTestCase.generate_scenarios()
 MachineReadableGeneratorTestCase.generate_scenarios()

oslo_config/types.py

@@ -871,6 +871,13 @@ class HostDomain(HostAddress):
     # DOMAIN_REGEX is HOSTNAME_REGEX with the _ character added
     DOMAIN_REGEX = '(?!-)[A-Z0-9-_]{1,63}(?<!-)$'
 
+    def __init__(self, version=None, type_name='host domain value'):
+        """Check for valid version in case an IP address is provided
+
+        """
+
+        super(HostDomain, self).__init__(type_name=type_name)
+
     def __call__(self, value):
         """Checks if is a valid IP/hostname.
 

releasenotes/notes/add-missing-config-option-9ee1992eea750200.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Adding the missing ``HostDomain`` config option. Previously this available
+    type couldn't been imported because no related config option was defined.