node: improve GetActiveHandles performance

Improve performance of process._getActiveHandles by sending handles in
batches to JS to be set on the passed Array. Add test to check proper
active handles are returned.

Alter implementation of GetActiveRequests to match GetActiveHandles'
implementation.

PR-URL: https://github.com/nodejs/node/pull/3780


Reviewed-By: Fedor Indutny <fedor@indutny.com>