Fixing BulkProcessor2RetryIT

[masseyke]

BulkProcessor2RetryIT.testBulkRejectionLoadWithBackoff was failing for a couple of reasons:
(1) The test cluster sometimes intentionally times out requests, which can lead to failures.
(2) The client() method sometimes calls a method that triggers an assertion failure if you're running in a transport thread (which part of our test is):

        java.lang.AssertionError: Expected current thread [Thread[elasticsearch[node_s2][transport_worker][T#1],5,TGRP-BulkProcessor2RetryIT]] to not be a transport thread. Reason: [Blocking operation]
            at __randomizedtesting.SeedInfo.seed([7979906EFF34169B]:0)
            at org.elasticsearch.transport.Transports.assertNotTransportThread(Transports.java:56)
            at org.elasticsearch.common.util.concurrent.BaseFuture.blockingAllowed(BaseFuture.java:80)
            at org.elasticsearch.common.util.concurrent.BaseFuture.get(BaseFuture.java:74)
            at org.elasticsearch.common.util.concurrent.FutureUtils.get(FutureUtils.java:45)
            at org.elasticsearch.action.support.AdapterActionFuture.actionGet(AdapterActionFuture.java:26)
            at org.elasticsearch.action.support.PlainActionFuture.get(PlainActionFuture.java:24)
            at org.elasticsearch.transport.TransportService.openConnection(TransportService.java:483)
            at org.elasticsearch.client.transport.TransportClientNodesService$SimpleNodeSampler.doSample(TransportClientNodesService.java:413)
            at org.elasticsearch.client.transport.TransportClientNodesService$NodeSampler.sample(TransportClientNodesService.java:364)
            at org.elasticsearch.client.transport.TransportClientNodesService.addTransportAddresses(TransportClientNodesService.java:200)
            at org.elasticsearch.client.transport.TransportClient.addTransportAddress(TransportClient.java:416)
            at org.elasticsearch.test.InternalTestCluster$TransportClientFactory.client(InternalTestCluster.java:1224)
            at org.elasticsearch.test.InternalTestCluster$NodeAndClient.getOrBuildTransportClient(InternalTestCluster.java:1040)
            at org.elasticsearch.test.InternalTestCluster$NodeAndClient.client(InternalTestCluster.java:994)
            at org.elasticsearch.test.InternalTestCluster.client(InternalTestCluster.java:849)
            at org.elasticsearch.test.ESIntegTestCase.client(ESIntegTestCase.java:677)
            at org.elasticsearch.test.ESIntegTestCase.client(ESIntegTestCase.java:670)
            at org.elasticsearch.action.bulk.BulkProcessor2RetryIT.countAndBulk(BulkProcessor2RetryIT.java:167)

This PR fixes both of those.
Closes #94452
Closes #94941

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[gmarouli]

LGTM, but please take into consideration that my knowledge is a bit shallow. If you just needed another pair of eyes, then all good :).

[gmarouli]

Is this TestLogging still useful? or should we remove it?

[masseyke]

I probably ought to remove it. I come here from time to time to grab this for use in other tests because I can never remember the syntax. :)