### Description

The `sendRequest` method is asynchronous and notifies a 
`TransportResponseHandler` when it completes the excecution
(successfully or unsuccessfully). 

When opening the connection we only catch `NodeNotConnectedException`
( https://github.com/elastic/elasticsearch/blob/main/server/src/main/java/org/elasticsearch/transport/TransportService.java#L719 ) which is currently fine as no implementations
throw other type of exception however, it'd be best to catch `Exception` here
so the `handler` gets notified of potential exceptions (as opposed to the caller
having to `try/catch` the call to `sendRequest`)
test/framework/src/main/java/org/elasticsearch/transport/AbstractSimpleTransportTestCase.java
return new TestResponse(in);
            }
            @Override
            public void handleResponse(TestResponse response) {
                logger.debug("---> received response: {}", response.info);
                allRequestsDone.countDown();
            }
            @Override
            public void handleException(TransportException exp) {
                logger.debug((Supplier<?>) () -> "---> received exception for id " + id, exp);
                allRequestsDone.countDown();
                Throwable unwrap = ExceptionsHelper.unwrap(exp, IOException.class);
                assertNotNull(unwrap);
                assertEquals(IOException.class, unwrap.getClass());
                assertEquals("forced failure", unwrap.getMessage());
            }
            @Override
            public String executor() {
                return executor;
            }
        }
        for (int i = 0; i < iters; i++) {
            TransportService service = randomFrom(serviceC, serviceB, serviceA);
            DiscoveryNode node = randomFrom(nodeC, nodeB, nodeA);
            logger.debug("send from {} to {}", toNodeMap.get(service), node);
            service.sendRequest(
                node,
                "internal:action1",
                new TestRequest("REQ[" + i + "]"),
                TransportRequestOptions.EMPTY,