* GCE builder: Switch to google.DefaultClient
This enables authentication through an authenticated gcloud tool.
* GCE builder: Add docs about auth mech precedence
This change adds an `omit_external_ip` configuration property that, when true,
will cause no external IP address to be associated with the Google Compute
Engine VM provisioned to create an image. When using `omit_external_ip`, you
must also set the `use_internal_ip` configuration property to true.
Addresses #3296
- Startup scripts can be provided through the instance creation metadata field 'startup-script'.
- Script log can be copied to a GCS location by setting the metadata field 'startup-script-log-dest'.
Added Retry method to googlecompute package.
Added GetSerialPortOutput to googlecompute Drivers.
Added StepWaitInstanceStartup (and associated test) which waits for an
instance startup-script to finish.
Changed the instance service account to use the same service account as the one provided in the Packer config template. It was the project default service account.
Tested googlecompute package with 'go test' and also performed builds
with a startup script and without a startup script.