Use organisation API hostnames more helpfully

Hostnames in URLs returned by the Organisations API as api_id and
web_url for each organisation are dependent on the environment.
This change to the test helper makes that clearer, and also that
the api_id and web_url hostnames are different from each other.
Change 'acronym' to 'abbreviation' for organisations

This is to match the change made in Whitehall in e945dd6.
Merge pull request #81 from alphagov/orgs_api_updates

Organisations API adapter updates