Support SSH password authentication

SSH password authentication is quite common and with a strong password can be quite secure. Let's support it in docker-modem and dockerode.

lib/modem.js

@@ -75,6 +75,7 @@ var Modem = function (options) {
   this.host = opts.host;
   this.port = opts.port;
   this.username = opts.username;
+  this.password = opts.password;
   this.version = opts.version;
   this.key = opts.key;
   this.cert = opts.cert;
@@ -206,7 +207,7 @@ Modem.prototype.buildRequest = function (options, context, data, callback) {
   var connectionTimeoutTimer;
 
   var opts = self.protocol === 'ssh' ? Object.assign(options, {
-    agent: ssh({ 'host': self.host, 'port': self.port, 'username': self.username, 'agent': self.sshAuthAgent }),
+    agent: ssh({ 'host': self.host, 'port': self.port, 'username': self.username, 'password': self.password, 'agent': self.sshAuthAgent }),
     protocol: 'http:'
   }) : options;