Gryo reader / writer is broken in JanusGraph 1.0.0

As noted in the changelog: https://docs.janusgraph.org/changelog/#drop-support-for-gryo-messageserializer
Gryo MessageSerializer [has been dropped in TinkerPop 3.6.0](https://tinkerpop.apache.org/docs/3.6.1/upgrade/#_removed_gryo_messageserializers). However, TinkerPop documentation says that Gryo may still be used for file based applications.

For confirmed bugs, please report:

- Version: 1.0.0
- Storage Backend: -
- Mixed Index Backend: -
- Expected Behavior: file is created with `kryo` format.
- Current Behavior: an exception is thrown: `Method threw 'java.lang.IllegalArgumentException' exception.`.
- Steps to Reproduce:
Try to read or write any graph using kryo serialization.
```
g.io("graph.kryo").read().iterate()
g.io("graph.kryo").write().iterate()
```
### Stack Trace (if you have one)

```
Unable to create serializer "org.apache.tinkerpop.shaded.kryo.serializers.FieldSerializer" for class: java.util.concurrent.atomic.AtomicLong
```

Start by reproducing the `g.io("graph.kryo")` read and write operations and review the referenced TinkerPop Gryo removal documentation alongside the stack trace. Trace the reader and writer paths involved in Kryo serialization; done means both operations work without the serializer exception and produce the expected Kryo-format file.

Written by the indexing model from the issue text.