FulgoraGraphComputer fails with OOM

I try to run 'OLAPTest' for Aerospike storage backend.
'FulgoraGraphComputer' fails on this test when instantiate [large size ArrayList](https://github.com/JanusGraph/janusgraph/blob/15fe4143462a21994d417bd8e73b3cfba54157e8/janusgraph-core/src/main/java/org/janusgraph/graphdb/olap/computer/FulgoraGraphComputer.java#L312)
As I can see, large 'BUFFER_SIZE' parameter causes this error. [In case of Aerospike storage backend I set it to large value to avoid splitting of writes to bunches ](https://github.com/Playtika/aerospike-janusgraph-storage-backend/blob/develop/aerospike-storage-backend/src/main/java/com/playtika/janusgraph/aerospike/AerospikeStoreManager.java#L62)

Start by reproducing the OLAPTest failure with the Aerospike storage backend, then inspect the large ArrayList allocation around line 312 of janusgraph-core/src/main/java/org/janusgraph/graphdb/olap/computer/FulgoraGraphComputer.java. Compare it with the BUFFER_SIZE setting around line 62 of AerospikeStoreManager.java; done requires a defined change that prevents the OOM while preserving the backend's write behavior.

Written by the indexing model from the issue text.