s/CODENAME/GO_CLOUD
s/CODENAME/GO_CLOUD

Codename is no longer our internal codename. It's now go-cloud, and that
should be reflected in the variable naming.

Change-Id: Iced403ca9af9e86b3d012c20427a7ef6445f54c6
Reviewed-on: https://team-review.git.corp.google.com/251792
Reviewed-by: Tuo Shan <e38988508c7dd9b59ee1f5735040284711960df8@google.com>

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