Fix sync and async testkit backends launch (neo4j#1027)

Author: injectives

testkit-backend/src/main/java/neo4j/org/testkit/backend/channel/handler/TestkitRequestProcessorHandler.java

@@ -51,13 +51,13 @@ public TestkitRequestProcessorHandler( BackendMode backendMode )
         switch ( backendMode )
         {
         case ASYNC:
-            processorImpl = TestkitRequestProcessorHandler::wrapSyncRequest;
+            processorImpl = TestkitRequest::processAsync;
             break;
         case REACTIVE:
             processorImpl = ( request, state ) -> request.processRx( state ).toFuture();
             break;
         default:
-            processorImpl = TestkitRequest::processAsync;
+            processorImpl = TestkitRequestProcessorHandler::wrapSyncRequest;
             break;
         }
     }