compute/metadata: also recognize "Google Compute Engine" as an on-GCE hint
compute/metadata: also recognize "Google Compute Engine" as an on-GCE hint

People seem to want to move towards the more specific string.

Change-Id: I924e689d550dd516f46166179498de33461956ca
Reviewed-on: https://code-review.googlesource.com/5380
Reviewed-by: Dave Day <4cba7a21e1f1fc896442779dcb55aeda6df97dfe@golang.org>

googleapis/google-cloud-go,michael-grosshans/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,michael-grosshans/google-cloud-go,googleapis/google-cloud-go