Fix random failure in ChangelogBackendTestCase

searchInCookieModeOnTwoSuffixes(org.opends.server.backends.ChangelogBackendTestCase)  Time elapsed: 0.731 sec  <<< FAILURE!
java.lang.AssertionError:
Expecting:
 <[0000014f2d08a87f04b200000003]>
to contain exactly (and in same order):
 <[0000014f2d08a87f04b100000004]>
but some elements were not found:
 <[0000014f2d08a87f04b100000004]>
and others were not expected:
 <[0000014f2d08a87f04b200000003]>
	at org.opends.server.backends.ChangelogBackendTestCase.assertEntriesContainsCSNsAndReadLastCookie(ChangelogBackendTestCase.java:966)
	at org.opends.server.backends.ChangelogBackendTestCase.searchInCookieModeOnTwoSuffixes(ChangelogBackendTestCase.java:403)