title: Corda service does not exist when running flow tests with a MockNetwork
body: <p>I have a CorDapp where I define an oracle. The oracle works fine when running the nodes normally. However, when running flow tests using a MockNetwork, I get the following exception:</p>
  
  <blockquote>
    <p>net.corda.core.flows.FlowException:
    java.lang.IllegalArgumentException: Corda service
    net.corda.option.oracle.oracle.Oracle does not exist</p>
  </blockquote>
  
  <p>How can I register the Corda service with the <code>MockNetwork</code> or get it to recognise it?</p>