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
bb5e4cbeb9