title: Change UISearchBar background image in iOS11
body: <p>I want to change my UISearchBar background image.
  When adding it as the header view in my UITableView it works perfectly fine. However, when I want to change it for the SearchBar being set as the searchController of the navigationItem it won´t change the background image.</p>
  
  <p>I´m using:</p>
  
  <pre><code>self.searchBar.searchBar.setBackgroundImage(UIImage(named: "#IMAGENAME")?.resizableImage(withCapInsets: UIEdgeInsets.zero, resizingMode: .stretch), for: .any, barMetrics: UIBarMetrics.default)
  </code></pre>
  
  <p>Does anybody know how to fix this issue?</p>