## 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.
response.getOutputStream().print(updatedTemplate);
      }
    }
    response.flushBuffer();
  }
  private void initServletConfig() {
    if (servletConfig.version == null) {
      servletConfig.version = new BuildInfo().getReleaseLabel();
    }
    if (servletConfig.type == null) {
      servletConfig.type = getHelperType();
    }
    if (servletConfig.consoleLink == null) {
      
      
      servletConfig.consoleLink = getInitParameter(ConsoleServlet.CONSOLE_PATH_PARAMETER, "");
    }
  }
  private String getHelperType() {
    GridRole role = GridRole.get(getInitParameter(HELPER_TYPE_PARAMETER, "standalone"));
    if (role == null) {
      role = GridRole.NOT_GRID;
    }
    String type = "Standalone";
    switch (role) {
      case HUB: {
        type = "Grid Hub";
        break;
      }
      case NODE: {