Improve docs in gnome_remote_desktop source

Add information about possible raised exception.

pyanaconda/gnome_remote_desktop.py

@@ -164,6 +164,8 @@ def _get_hostname_in_thread(ip, stdout_log):
 
         This call will be done from the thread to avoid situations where DNS is too slow or
         doesn't exists and we are waiting for the reply about 2 minutes.
+
+        :raises: ValueError and socket.herror
         """
         try:
             hinfo = socket.gethostbyaddr(ip)