BlobStoreCompactor test failure

[cgtz]

Got the following test failure on the most recent travis build.

com.github.ambry.store.BlobStoreCompactorTest > interruptionDuringLastCommitTest FAILED
    java.lang.AssertionError: Last modified time of an older index segment > newer index segment
        at org.junit.Assert.fail(Assert.java:91)
        at org.junit.Assert.assertTrue(Assert.java:43)
        at com.github.ambry.store.CuratedLogIndexState.verifyRealIndexSanity(CuratedLogIndexState.java:616)
        at com.github.ambry.store.CuratedLogIndexState.verifyState(CuratedLogIndexState.java:860)
        at com.github.ambry.store.CuratedLogIndexState.setupTestState(CuratedLogIndexState.java:766)
        at com.github.ambry.store.CuratedLogIndexState.<init>(CuratedLogIndexState.java:181)
        at com.github.ambry.store.BlobStoreCompactorTest.refreshState(BlobStoreCompactorTest.java:937)
        at com.github.ambry.store.BlobStoreCompactorTest.interruptionDuringLastCommitTest(BlobStoreCompactorTest.java:694)

[vgkholla]

The compaction code has not run at this point. This happened during the setup of the test (create a log, index etc). I'll add some log messages but this seems super rare (this piece of code runs on the startup of every single index and compactor test), so its hard to repro. I'll also go through the index persistence code to spot any bugs.

[vgkholla]

@cgtz #856