Fix rocksdb oom with g.V().hasLabel().count() (#823)

Fix rocksdb oom with g.V().hasLabel().count() (#823)

* fix iter gloabal
* Manually close the iterators
* catch locks in every batch
* limit iterator to list
* improve cache iter
* fix system index-label graph() return null
* add QueryResults.one() method
* fix BatchIdHolder dead loop with batchSize=0
* fix test iterators don't be closed
* add option query.batch_size
* force limit BatchIdHolder.all()
* adapt ListIterator.list() return Collection<T>
* set default value of check_customized_id_exist option to false
* fix cassandra oom
* fix offset bug
* Increase limit for intersection
* fix check subRows().size() <= INLINE_BATCH_SIZE

Change-Id: I13daaa513b2f5ddc69bcae4d548f263ad1f5b08d