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
`cares` should have been bound at https://github.com/joyent/node/blob/v0.12/lib/dns.js#L25, and it is not yet used in this test.