src: don't abort when c-ares initialization fails

Throw a JS exception instead of aborting so the user at least has a
fighting chance of understanding what went wrong.

Fixes: https://github.com/nodejs/node/issues/8699
PR-URL: https://github.com/nodejs/node/pull/8710


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>