GCE installs some Python-2-only boto plugin that conflicts with boto running under Python 3. It gives a SyntaxError in /usr/share/google/boto/boto_plugins/compute_auth.py (https://github.com/GoogleCloudPlatform/compute-image-packages).

Disabling boto's default configuration file prior to importing boto so that GCE's plugin is not loaded.

See https://discourse.mailinabox.email/t/500-internal-server-error-for-admin/942.