Feat/update fail if no pacts found pr

[YOU54F]

fixes #272

continuation of #283

Usage

Pact.service_provider 'your-provider-name' do
  honours_pacts_from_pact_broker do
    pact_broker_base_url '<pact_broker_url>'
    fail_if_no_pacts_found false # defaults to true
  end
end