Make http.request correctly parse {host: "hostname:port"}

The issue:
http.request() treats host as an alternate form of hostname, which
it sort of is, except that host is (normally) allowed to contain a
port number.

Before this change, if host contains a port number and there isn't
a hostname field to override it, http.request() attempts a DNS
lookup on the entire host field, including the port number. This
always fails.

The fix:
If a host field is present, use the url lib to parse it and use
the parsed hostname nad port values as fallbacks if
options.hostname and options.port are unset.

Includes tests for localhost:12346 and [::1]:12346.

lib/_http_client.js

@@ -57,8 +57,19 @@ function ClientRequest(options, cb) {
   const defaultPort = options.defaultPort ||
                       self.agent && self.agent.defaultPort;
 
-  var port = options.port = options.port || defaultPort || 80;
-  var host = options.host = options.hostname || options.host || 'localhost';
+  const parsedHost = {host: options.host};
+  if (options.host) {
+    url.Url.prototype.parseHost.call(parsedHost);
+
+    // unwrap brackets from ipv6 ip addresses
+    const hostname = parsedHost.hostname;
+    if (hostname[0] === '[' && hostname[hostname.length - 1] === ']') {
+      parsedHost.hostname = hostname.substr(1, hostname.length - 2);
+    }
+  }
+
+  const port = options.port = options.port || parsedHost.port || defaultPort || 80;
+  const host = options.host = options.hostname || parsedHost.hostname || 'localhost';
 
   if (options.setHost === undefined) {
     var setHost = true;

test/parallel/test-http-request-host-port-ipv6.js

@@ -0,0 +1,34 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+
+if (!common.hasIPv6) {
+    console.log('1..0 # Skipped: no IPv6 support');
+    return;
+}
+
+var connected = false;
+
+const server = http.createServer(function(req, res) {
+  connected = true;
+  res.writeHead(204);
+  res.end();
+});
+
+server.listen(common.PORT, '::1', function() {
+ http.get({
+    host: '[::1]:' + common.PORT
+  }, function(res) {
+    res.resume();
+    server.close();
+  }).on('error', function(e) {
+    throw e;
+  });
+});
+
+process.on('exit', function() {
+  assert(connected, 'http.request should correctly parse ' +
+      '{host: "hostname:port"} and connect to the specified host');
+});

test/parallel/test-http-request-host-port.js

@@ -0,0 +1,29 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+
+var connected = false;
+
+const server = http.createServer(function(req, res) {
+  connected = true;
+  res.writeHead(204);
+  res.end();
+});
+
+server.listen(common.PORT, function() {
+ http.get({
+    host: 'localhost:' + common.PORT
+  }, function(res) {
+    res.resume();
+    server.close();
+  }).on('error', function(e) {
+    throw e;
+  });
+});
+
+process.on('exit', function() {
+  assert(connected, 'http.request should correctly parse ' +
+      '{host: "hostname:port"} and connect to the specified host');
+});