dns: propagate domain for c-ares methods

Per https://github.com/joyent/node/issues/5471, domains were not being propagated for certain dns methods (those using `class Query` in `cares_wrap.cc`). This rectifies the situation.

/cc @trevnorris
Ah, interesting. I don't think jslint was run against the tests/ directory as part of `make test`. Sorry -- fixing now.