Add connection edge case integration tests

We discovered that there is a bug with which strategy each error has to have. Connection refused or connection reset are not retried on UDS Connections.

lib/datadog/statsd/uds_connection.rb

@@ -28,6 +28,9 @@ def send_message(message)
         socket.sendmsg_nonblock(message)
       rescue Errno::ECONNREFUSED, Errno::ECONNRESET, Errno::ENOENT => e
         @socket = nil
+        # TODO: FIXME: This error should be considered as a retryable error in the
+        # Connection class. An even better solution would be to make BadSocketError inherit
+        # from a specific retryable error class in the Connection class.
         raise BadSocketError, "#{e.class}: #{e}"
       end
     end