add error when socket.gethostbyadder() failed
(rtm.py) Error message minor improvement
Merge pull request #1 from 130s/add_error_on_could_not_find_hostname

(rtm.py) Error message minor improvement
Merge pull request #248 from k-okada/add_error_on_could_not_find_hostname

add error message when socket.gethostbyadder() failed