fix(constructor): set username, password, database via options (#9517)

lib/sequelize.js

@@ -195,14 +195,10 @@ class Sequelize {
 
     this._setupHooks(options.hooks);
 
-    if (['', null, false].indexOf(config.password) > -1 || typeof config.password === 'undefined') {
-      config.password = null;
-    }
-
     this.config = {
-      database: config.database,
-      username: config.username,
-      password: config.password,
+      database: config.database || this.options.database,
+      username: config.username || this.options.username,
+      password: config.password || this.options.password || null,
       host: config.host || this.options.host,
       port: config.port || this.options.port,
       pool: this.options.pool,

test/unit/configuration.test.js

@@ -121,6 +121,20 @@ describe('Sequelize', () => {
       expect(config.password).to.be.null;
     });
 
+    it('should correctly set the username, the password and the database through options', () => {
+      const options = {
+        username: 'root',
+        password: 'pass',
+        database: 'dbname'
+      };
+      const sequelize = new Sequelize('mysql://example.com:9821', options);
+      const config = sequelize.config;
+
+      expect(config.username).to.equal(options.username);
+      expect(config.password).to.equal(options.password);
+      expect(config.database).to.equal(options.database);
+    });
+
     it('should use the default port when no other is specified', () => {
       const sequelize = new Sequelize('dbname', 'root', 'pass', {
           dialect