Remove defaults for integration test config values

They don't help as the defauts are not valid on test environments.
Removing them moves us towards failing with clearer errors for users
of the tests
rename integration test config values

Use better names to guide people to select working values so people
can run the integration tests on their environments
Merge pull request #75 from alphagov/the_defaults_dont_work

The defaults don't work, they just make it worse