Flaky Test EmbeddedLogTest testLogIsDurableAcrossReopenSerial

## Flaky Test

* **Test Name:** org.janusgraph.diskstorage.cassandra.embedded.EmbeddedLogTest#testLogIsDurableAcrossReopenSerial
* **Link:** https://github.com/JanusGraph/janusgraph/blob/89f6c69a8d98c5ea71ae3944e01ed80b801658a5/janusgraph-backend-testutils/src/main/java/org/janusgraph/diskstorage/log/LogTest.java#L124
* **Branch:** master
* **Notes:** Looks like the test is fluky due to usage of timeout
### Stack Trace

```
[INFO] Running org.janusgraph.diskstorage.cassandra.embedded.EmbeddedLogTest

SLF4J: Class path contains multiple SLF4J bindings.

SLF4J: Found binding in [jar:file:/home/travis/.m2/repository/org/slf4j/slf4j-log4j12/1.7.12/slf4j-log4j12-1.7.12.jar!/org/slf4j/impl/StaticLoggerBinder.class]

SLF4J: Found binding in [jar:file:/home/travis/.m2/repository/ch/qos/logback/logback-classic/1.1.3/logback-classic-1.1.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]

SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.

SLF4J: Actual binding is of type [org.slf4j.impl.Log4jLoggerFactory]

[ERROR] Tests run: 14, Failures: 1, Errors: 0, Skipped: 2, Time elapsed: 102.568 s <<< FAILURE! - in org.janusgraph.diskstorage.cassandra.embedded.EmbeddedLogTest

[ERROR] testLogIsDurableAcrossReopenSerial Time elapsed: 30.312 s <<< FAILURE!

java.lang.AssertionError: Did not read expected number of messages before timeout was reached (latch count is 1)

[INFO]

[INFO] Results:

[INFO]

[ERROR] Failures:

[ERROR] EmbeddedLogTest>LogTest.testLogIsDurableAcrossReopenSerial:138 Did not read expected number of messages before timeout was reached (latch count is 1)

[INFO]

[ERROR] Tests run: 14, Failures: 1, Errors: 0, Skipped: 2
```

Start with the referenced test in janusgraph-backend-testutils/src/main/java/org/janusgraph/diskstorage/log/LogTest.java around line 124, then run org.janusgraph.diskstorage.cassandra.embedded.EmbeddedLogTest#testLogIsDurableAcrossReopenSerial. Investigate the timeout and latch-count failure, and consider the issue complete when this test runs reliably without the reported timeout failure.

Written by the indexing model from the issue text.