tests: Clean up instance object names that are the same as the class they instance from.

[ryanseys]

As per this discussion instance objects should use a slightly different name than the class name that they are instanced from. Not a big issue at all, just a nit.

[ryanseys]

I'm closing this because I disagree with past self now about this issue. We specifically promote this type of activity with out var datastore = gcloud.datastore(); patterns.