code: func (c *dbinitCmd) mongoSession() (*mgo.Session, error) {
  	if c.dbType != "mongo" {
  		return nil, nil
  	}
  	url := ""
  	if c.user == "" || c.password == "" {
  		url = c.host
  	} else {
  		url = c.user + ":" + c.password + "@" + c.host + "/" + c.dbName
  	}
  	return mgo.Dial(url)
  }
docs: // mongoSession returns an *mgo.Session or nil if c.dbtype is
  // not "mongo" or if there was an error.