benchmark: fix issues in dns

The benchmark script for dns contained functions with args declared
but never used. This fix removes those arguments from the function
signatures.

No test existed for the dns benchmark so one was added to the
parallel suite.

The dns benchmark uses the core dns.lookup() function which does not
access the network.

To improve performance the tests are limited to 1 invocation to a
single endpoint.

Author: keondo

benchmark/dns/lookup.js

@@ -12,7 +12,7 @@ const bench = common.createBenchmark(main, {
 function main(conf) {
   const name = conf.name;
   const n = +conf.n;
-  const all = !!conf.all;
+  const all = conf.all === 'true' ? true : false;
   var i = 0;
 
   if (all) {

test/parallel/test-benchmark-dns.js

@@ -15,7 +15,9 @@ const env = Object.assign({}, process.env,
                           { NODEJS_BENCHMARK_ZERO_ALLOWED: 1 });
 
 const child = fork(runjs,
-                   ['--set', 'n=5e4',
+                   ['--set', 'n=1',
+                    '--set', 'all=false',
+                    '--set', 'name=127.0.0.1',
                     'dns'],
                    { env });