Removed the ability to manually start notary nodes from the driver and MockNetwork. Instead by default a single notary is automatically started. This can be customised at creation time of the driver and MockNetwork. This more accurately models the concept of network parameters in a CZ.

Also added helper methods to retrieve this default notary.

docs/source/example-code/src/integration-test/kotlin/net/corda/docs/IntegrationTestingTutorial.kt

@@ -37,8 +37,7 @@ class IntegrationTestingTutorial {
                     invokeRpc("vaultTrackBy"),
                     invokeRpc(CordaRPCOps::networkMapFeed)
             ))
-            val (_, alice, bob) = listOf(
-                    startNotaryNode(DUMMY_NOTARY.name),
+            val (alice, bob) = listOf(
                     startNode(providedName = ALICE.name, rpcUsers = listOf(aliceUser)),
                     startNode(providedName = BOB.name, rpcUsers = listOf(bobUser))
             ).transpose().getOrThrow()