avoid bare `except:`s in grains/external_ip.py

************* Module salt.grains.external_ip
salt/grains/external_ip.py:4: [W0702(bare-except), ] No exception type(s) specified
salt/grains/external_ip.py:18: [W0702(bare-except), external_ip] No exception type(s) specified
Merge pull request #9167 from cvrebert/patch-2

avoid bare `except:`s in grains/external_ip.py