Add Node 10 support

[pierceray]

We need to add support for node 10 (Dubnium).

[jared-stilwell]

It seems like the timing of the promises in the unit tests shift in subtle ways starting in node 10.5 but it isn't obvious exactly what is causing the unit tests to not complete successfully. It seems like untangling the tests that use node-tap autocompletion and return promise objects to not have a return value and use an explicit t.end() is a starting point to simplifying matters and perhaps eliminating whatever the issue is altogether.