## Meta
OS:  macOS
Selenium Version:  3.11, code indicates this should be in master still
Browser:  Chrome

## Expected Behavior
When visiting a page/servlet that does not exist in Grid, a 404 status code should be returned.

## Actual Behavior
A 200 status code is returned for pages that do not exist.

## Steps to reproduce
1) Launch a hub or node
2) Open your browser's network tab
3) Visit localhost:4444/thisdoesntexist

```
Request URL: http://localhost:4444/thisdoesntexist
Request Method: GET
Status Code: 200 OK
```

## More Information
It appears the design for any [non-registered routes](https://github.com/SeleniumHQ/selenium/blob/5457171bd52747eed2ab625607d29670448f4523/java/server/src/org/openqa/grid/selenium/GridLauncherV3.java#L270) to direct to `DisplayHelpServlet`, which [returns the 200](https://github.com/SeleniumHQ/selenium/blob/5457171bd52747eed2ab625607d29670448f4523/java/server/src/org/openqa/grid/web/servlet/DisplayHelpServlet.java#L122).

Considering I typed a page that should not exist, I feel it may be more obvious if a 404 is returned to indicate a problem.

Context: My application was requesting a custom servlet by the wrong name, and became confused when a 200 was returned but the proper action did not occur. A 404 would have very quickly jumped out as a route issue.
String version;
    String type;
    String consoleLink;
    public String getVersion() {
      return version;
    }
    public String getType() {
      return type;
    }
    public String getConsoleLink() {
      return consoleLink;
    }
  }
  private final DisplayHelpServletConfig servletConfig = new DisplayHelpServletConfig();
  @Override
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws IOException {
    process(request, response);
  }
  @Override
  protected void doPost(HttpServletRequest request, HttpServletResponse response)
      throws IOException {
    process(request, response);
  }
  protected void process(HttpServletRequest request, HttpServletResponse response)
      throws IOException {
    initServletConfig();
    String resource = request.getPathInfo();
    InputStream in;