fix: fail early if no pacts found for verification

[YOU54F]

fixes #411

[bekasovoleg]

LGTM 👍🏻

minor: provider/consumer names aren't consistent across the pact tests - the same app gets different names - might be worth keeping the names in sync and use the same name everywhere - u2y

  - http_client_spec.rb - 'pact-ruby-test-app', 'pact-ruby-test-app'
  - grpc_client_spec.rb - 'pact-ruby-test-app', 'pact-ruby-test-app'
  - message_spec.rb - 'Test Message Consumer', 'Test Message Provider'
  - kafka_spec.rb - 'pact-ruby-test-app', 'pact-ruby-test-app-kafka'
  - plugin_matt_http_spec.rb - 'myconsumer', 'myprovider'
  - plugin_matt_sync_message_spec.rb - 'myconsumer', 'myprovider'
  - plugin_matt_async_message_spec.rb - 'matttcpconsumer', 'matttcpprovider'
  - plugin_grpc_sync_message_spec.rb - 'pact-ruby-test-app', 'pact-ruby-test-app'