Fix random in TestLogChronicle.testConcurrentFileRetentions

org.nuxeo.lib.stream.tests.log.TestLogChronicle.testConcurrentFileRetentions (from org.nuxeo.lib.stream.tests.computation.TestLogStreamProcessorKafka)
Failing for the past 1 build (Since Unstable#611 )
Took 6.2 sec.
add description
Error Message

expected:<LogLag{lower=0, upper=15, lag=15, lowerOffset=0, upperOffset=15}> but was:<LogLag{lower=0, upper=10, lag=10, lowerOffset=6498898930372182016, upperOffset=6498898938962116613}>

Stacktrace

java.lang.AssertionError: expected:<LogLag{lower=0, upper=15, lag=15, lowerOffset=0, upperOffset=15}> but was:<LogLag{lower=0, upper=10, lag=10, lowerOffset=6498898930372182016, upperOffset=6498898938962116613}>
	at org.junit.Assert.fail(Assert.java:88)
	at org.junit.Assert.failNotEquals(Assert.java:834)
	at org.junit.Assert.assertEquals(Assert.java:118)
	at org.junit.Assert.assertEquals(Assert.java:144)
	at org.nuxeo.lib.stream.tests.log.TestLogChronicle.testConcurrentFileRetentions(TestLogChronicle.java:164)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)