tracereport: also catch gaierror for gethostbyaddr()

[olifre]

socket.gethostbyaddr() throws a socket.gaierror exception if the address can not be resolved which was not caught before.

Fixes regression introduced by e7d7c6f , after which Pilot yielded stage-in and stage-out errors with backtrace for sites using a non-DNS resolvable PANDA_HOSTNAME (VMs, long-lived containers,...).

[olifre]

Example Python script illustrating the problem:

#!/usr/bin/python3

import os
import socket

try:
    socket.gethostbyaddr("does_not_resolve")[0]
except socket.herror as exc:
    print("caught")

This yields:

Traceback (most recent call last):
  File "check_ip_bad.py", line 7, in <module>
    socket.gethostbyaddr("does_not_resolve")[0]
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
socket.gaierror: [Errno -2] Name or service not known

[PalNilsson]

Thanks but please make the PR to the next branch instead.

[olifre]

@PalNilsson Sure, done: #117