test: use .test domain for not found address

While it is extremely unlikely that `.fhqwhgads` will become a valid
domain, we should, where possible, use one of the reserved domains for
testing.

Refs: https://tools.ietf.org/html/rfc2606

Author: richardlau

test/common/internet.js

@@ -24,7 +24,7 @@ const addresses = {
   MX_HOST: 'nodejs.org',
   // On some systems, .invalid returns a server failure/try again rather than
   // record not found. Use this to guarantee record not found.
-  NOT_FOUND: 'come.on.fhqwhgads',
+  NOT_FOUND: 'come.on.fhqwhgads.test',
   // A host with SRV records registered
   SRV_HOST: '_jabber._tcp.google.com',
   // A host with PTR records registered