Allow remote network requests
Allow remote network requests

The gds-api-adapters build was passing, but the pact tests weren't
actually passing: https://ci.integration.publishing.service.gov.uk/job/gds-api-adapters/job/master/404/console
Webmock wants us to stub all network requests, by default. But in
the case of Pact tests, we need to communicate with the Pact broker
over HTTP, so we actually want to enable network requests in this case.

Relevant output from the logs:

```
  Given there is a list of all bank holidays
    the request for the list of all bank holidays
      with GET /bank-holidays.json
        returns a response which
          has status code 200
          has a matching body
          includes headers
            "Content-Type" which equals "application/json; charset=utf-8"
Error making request - WebMock::NetConnectNotAllowedError Real HTTP connections are disabled. Unregistered request: GET https://pact-broker.cloudapps.digital/pacts/provider/Bank%20Holidays%20API/consumer/GDS%20API%20Adapters/version/master/diff/previous-distinct with headers {'Accept'=>'text/plain', 'Accept-Encoding'=>'gzip;q=1.0,deflate;q=0.6,identity;q=0.3', 'User-Agent'=>'Ruby'}

You can stub this request with the following snippet:

stub_request(:get, "https://pact-broker.cloudapps.digital/pacts/provider/Bank%20Holidays%20API/consumer/GDS%20API%20Adapters/version/master/diff/previous-distinct").
  with(
    headers: {
	  'Accept'=>'text/plain',
	  'Accept-Encoding'=>'gzip;q=1.0,deflate;q=0.6,identity;q=0.3',
	  'User-Agent'=>'Ruby'
    }).
  to_return(status: 200, body: "", headers: {})
```

I did wonder if `checkoutDependent` was not returning the exit
code correctly: https://github.com/alphagov/govuk-jenkinslib/blob/a5957a0cceb0aac4dc88aabd9497a5040e2dea17/vars/govuk.groovy#L416-L434

However, I tried checking out Frontend locally and running
`bundle exec rake pact:verify:branch[master]` and reproduced the issue,
and determined that it was exiting with a success exit code:

```
  to_return(status: 200, body: "", headers: {})
  ============================================================

2 interactions, 0 failures
```

So the underlying problem seems to be with the Pact gem, rather
than our implementation.

alphagov/frontend,alphagov/frontend,alphagov/frontend,alphagov/frontend