Redirector sites

Tests for checking the home page redirects for sites where the DNS points at the redirector. 

Other tests against preview are used to ensure the integrity of the mappings, this is primarily intended to ensure the DNS is in place, and the redirector running and available.

The tests are generated by the [tools/generate_smokey_tests](https://github.com/alphagov/redirector/blob/master/tools/generate_smokey_tests.sh) script from [data/sites.csv](https://github.com/alphagov/redirector/blob/master/data/sites.csv).

The redirect for a site's primary domain is marked with a priority of `high`, and aliases for the site as `normal` with DirectGov, Business Link and the MOD marked as `urgent`. 

The timeout is now 2 instead of 1 seconds to reduce the possibility of waking people up unnecessarily.

It's possible these tests could be written more idiomatically, probably using cucumber tables, but I think I prefer the tests to be blanked out in full.