Using service account scopes as E. Anderson mentions is the recommended way to use gsutil on Compute Engine, so the images are configured to get OAuth access tokens from the metadata server in /etc/boto.cfg:
[GoogleCompute]
service_account = default
If you want to manage gsutil config yourself, rename /etc/boto.cfg, and gsutil config
should work:
$ sudo mv /etc/boto.cfg /etc/boto.cfg.orig
$ gsutil config
This script will create a boto config file at
/home/<...snipped...>/.boto
containing your credentials, based on your responses to the following questions.
<...snip...>