Diagnostics for FlowDurabilityTest

[jglick]

Get occasional flakes in CI in FlowDurabilityTest.testPauseForcesLowDurabilityToPersist and some others (CloudBees-internal reference) that I do not understand:

org.junit.runners.model.TestTimedOutException: test timed out after 180 seconds
	at [email protected]/java.lang.Object.wait(Native Method)
	at app//org.jenkinsci.plugins.workflow.job.WorkflowRun$Owner.get(WorkflowRun.java:985)
	at app//org.jenkinsci.plugins.workflow.flow.FlowExecutionList.resume(FlowExecutionList.java:226)
	at app//org.jenkinsci.plugins.workflow.flow.FlowExecutionList$ItemListenerImpl.onLoaded(FlowExecutionList.java:217)
	at app//jenkins.model.Jenkins.<init>(Jenkins.java:1070)
	at …

After the restart, there are no warnings about the test build, and nothing in the log beyond

   0.612 [id=279]	INFO	jenkins.InitReactorRunner$1#onAttained: Completed initialization
 180.001 [id=1]	WARNING	o.j.hudson.test.JenkinsRule$2#evaluate: Test timed out (after 180 seconds).
 180.002 [id=263]	WARNING	o.j.p.w.job.WorkflowRun$Owner#get: failed to wait for durableAgainstClean #1 to be loaded
java.lang.InterruptedException
	at java.base/java.lang.Object.wait(Native Method)
	at org.jenkinsci.plugins.workflow.job.WorkflowRun$Owner.get(WorkflowRun.java:985)
	at …

and no other threads active. It is as if RunMap.retrieve calls reload (via <init>) but not onLoad? No real hypothesis at this point. The test cases in this class generally are clearly prone to flakiness (see the various sleep steps and Thread.sleep calls with no guard) but seem potentially important so I am reluctant to just disable them.

[jglick]

to pair with jenkinsci/workflow-job-plugin#490