Add Gengo API tests and skip_if infrastructure

This adds some skip_if infrastructure for skipping tests if an
expression evaluates to True.

It also adds a couple of tests that actually execute the Gengo API calls
rather than executing against a mock Gengo API.

I should have done this when I did the machine translation changes.

r?
This is testing the gengo_api directly and that first argument is an instance id of the instance you're translating. 1010 is essentially "mock data".