compute/metadata: InstanceName returns actual instance name
compute/metadata: InstanceName returns actual instance name

(instead of first part of hostname)

Fixes #1698

Change-Id: I41a9beb2df4e00b420a6ff3f42297504148f0228
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/49330
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Tyler Bui-Palsulich <b41e4aa57d2ad7eb1b29835a1b483e209dcc3c0e@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go