Flaky CQL test dropGraphShouldRemoveGraphKeyspace

## Flaky Test

* **Test Name:** CQLConfiguredGraphFactoryTest.dropGraphShouldRemoveGraphKeyspace
* **Link:** https://github.com/JanusGraph/janusgraph/blob/d92fe83d9e0a709102aaf9e86debef7fa4608609/janusgraph-cql/src/test/java/org/janusgraph/core/cql/CQLConfiguredGraphFactoryTest.java#L112
* **Branch:** master
* **Notes:**

### Stack Trace

```
Error: Failures:
Error: CQLConfiguredGraphFactoryTest.dropGraphShouldRemoveGraphKeyspace:127 expected: but was:
```

Open janusgraph-cql/src/test/java/org/janusgraph/core/cql/CQLConfiguredGraphFactoryTest.java at the dropGraphShouldRemoveGraphKeyspace test and examine the assertion at line 127. Run this test to reproduce the reported row-versus-null result; done means the graph keyspace is reliably absent after the drop and the test passes without flaking.

Written by the indexing model from the issue text.