Intermittent Test failure: VcrBackupTest.singleNodeUpDownTestWithoutPersist "Blob count is not correct"

[cgtz]

Failed on travis build once, and then succeeded on the next attempt:

com.github.ambry.server.VcrBackupTest > singleNodeUpDownTestWithoutPersist FAILED
    java.lang.AssertionError: Blob count is not correct.
        at org.junit.Assert.fail(Assert.java:89)
        at org.junit.Assert.assertTrue(Assert.java:42)
        at com.github.ambry.server.VcrBackupTest.singleNodeUpDownTestWithoutPersist(VcrBackupTest.java:141)