Don't crash in perfdiag when nslookup is missing or gethostbyname fails.
Don't crash in perfdiag when nslookup is missing or gethostbyname fails.

GoogleCloudPlatform/gsutil,craigcitro/gsutil,fishjord/gsutil,BrandonY/gsutil,dimfeld/gsutil,ttiurani/gsutil,dtjackson/gsutil,chriskuehl/gsutil-debian,mattdr/gsutil,GoogleCloudPlatform/gsutil