Fix random in TestLogKafka#testSubscribe and TestLogStreamProcessorKafka#testSingleSource

Failed

org.nuxeo.lib.stream.tests.log.TestLogKafka.testSubscribe
Failing for the past 2 builds (Since Unstable#409 )
Took 0.65 sec.
add description
Error Message

expected:<997> but was:<667>

Stacktrace

junit.framework.AssertionFailedError: expected:<997> but was:<667>
	at junit.framework.Assert.fail(Assert.java:57)
	at junit.framework.Assert.failNotEquals(Assert.java:329)
	at junit.framework.Assert.assertEquals(Assert.java:78)
	at junit.framework.Assert.assertEquals(Assert.java:234)
	at junit.framework.Assert.assertEquals(Assert.java:241)
	at junit.framework.TestCase.assertEquals(TestCase.java:409)
	at org.nuxeo.lib.stream.tests.log.TestLogKafka.testSubscribe(TestLogKafka.java:263)