connection: normalize hostname in ConnectionOSErrorException

Use the existing helper to provide a properly formatted hostname for
user displaying (e.g. for exception); this will fix the printing of
IPv6 addresses.

Turn the existing "host" member as property, so the current users keep
working as expected.

Card ID: CCT-9

src/rhsm/connection.py

@@ -175,11 +175,15 @@ class ConnectionOSErrorException(ConnectionException):
     """
 
     def __init__(self, host: str, port: int, handler: str, exc: OSError):
-        self.host = host
+        self._host = host
         self.port = port
         self.handler = handler
         self.exc = exc
 
+    @property
+    def host(self) -> str:
+        return normalized_host(self._host)
+
 
 class ConnectionType(enum.Enum):
     """