Unable to run Cassandra tests

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Hi, I am trying to run the cql tests by following the steps mentioned here in the [ReadMe](https://github.com/JanusGraph/janusgraph/blob/master/TESTING.md).

I am unable to run the tests against Cassandra and am getting the following error for all of the test cases:
```
[ERROR] testBatchPropertiesPrefetching{int}[5] Time elapsed: 0.017 s <<< ERROR!
java.lang.IllegalArgumentException: Could not instantiate implementation: org.janusgraph.diskstorage.cql.CQLStoreManager
Caused by: java.lang.reflect.InvocationTargetException
Caused by: com.datastax.oss.driver.api.core.AllNodesFailedException: Could not reach any contact point, make sure you've provided valid addresses (showing first 2 nodes, use getAllErrors() for more): Node(endPoint=localhost/127.0.0.1:64096, hostId=null, hashCode=7bb2470b): [com.datastax.oss.driver.api.core.connection.ConnectionInitException: [JanusGraph Session|control|connecting...] Protocol initialization request, step 1 (OPTIONS): failed to send request (io.netty.channel.StacklessClosedChannelException)], Node(endPoint=localhost/0:0:0:0:0:0:0:1:64096, hostId=null, hashCode=7575b60d): [com.datastax.oss.driver.api.core.connection.ConnectionInitException: [JanusGraph Session|control|connecting...] Protocol initialization request, step 1 (OPTIONS): failed to send request (io.netty.channel.StacklessClosedChannelException)]
```

I am using Java SE 8, and am able to run the scyllaDB tests.

Start with TESTING.md and the CQL test setup described there, then reproduce the Cassandra failure involving CQLStoreManager and the localhost contact points. Check why Cassandra tests cannot connect while ScyllaDB tests run; done means the Cassandra test suite runs successfully with the documented Java SE 8 setup.

Written by the indexing model from the issue text.