Use FQDN for GCE metadata endpoint. (#7520)
Use FQDN for GCE metadata endpoint. (#7520)

Closes #7517.

tseaver/google-cloud-python,googleapis/google-cloud-python,GoogleCloudPlatform/gcloud-python,tswast/google-cloud-python,tseaver/google-cloud-python,tswast/google-cloud-python,tseaver/google-cloud-python,tswast/google-cloud-python,GoogleCloudPlatform/gcloud-python,googleapis/google-cloud-python