commandSuceedsWithoutChannel [sic] is flaky.

For example https://ci.jenkins-ci.org/job/jenkins_main_trunk/4281/testReport/hudson.slaves/CommandLauncherTest/commandSuceedsWithoutChannel/
java.lang.AssertionError: 
Expected: a string containing "ERROR: Process terminated with exit code 0"
     but: was "… Launching slave agent
$ true
ERROR: Unable to launch the slave agent for dummy
…java.io.EOFException: unexpected stream termination
	at hudson.remoting.ChannelBuilder.negotiate(ChannelBuilder.java:333)
	at hudson.remoting.ChannelBuilder.build(ChannelBuilder.java:282)
	at hudson.slaves.SlaveComputer.setChannel(SlaveComputer.java:365)
	at hudson.slaves.CommandLauncher.launch(CommandLauncher.java:130)
	at hudson.slaves.SlaveComputer$1.call(SlaveComputer.java:238)
	at jenkins.util.ContextResettingExecutorService$2.call(ContextResettingExecutorService.java:46)
	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
	at java.util.concurrent.FutureTask.run(FutureTask.java:166)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
	at java.lang.Thread.run(Thread.java:722)
"
	at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
	at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:8)
	at hudson.slaves.CommandLauncherTest.commandSuceedsWithoutChannel(CommandLauncherTest.java:67)