hasId does not convert int to Long

If an int is passed instead of a String or a Long to `hasId()` it does not get converted and results won't be yielded. This behavior has been report in issue #706, but I think this would be a nice improvement.

I think looking at the [HasStepFolder.foldInIds()](https://github.com/JanusGraph/janusgraph/blob/master/janusgraph-core/src/main/java/org/janusgraph/graphdb/tinkerpop/optimize/HasStepFolder.java#L118) method might be a good place to start.

Additional info can be found in this [stack overflow question](https://stackoverflow.com/questions/55912624/get-all-edges-between-multiple-vertices-janusgraph/55929179#55929179) and this
[tinkerpop issue](https://issues.apache.org/jira/browse/TINKERPOP-2209)

Start in janusgraph-core/src/main/java/org/janusgraph/graphdb/tinkerpop/optimize/HasStepFolder.java, particularly foldInIds(), and compare how int, String, and Long values are handled by hasId(). Reproduce the integer-id case using the linked context, then verify that integer inputs yield the same results as equivalent Long inputs.

Written by the indexing model from the issue text.