link_checker: Handle non-success status codes (#897)

The can_fail_404_links() test doesn't encounter a 404 response in
actuality, since the google.comys domain doesn't resolve. When the
test is updated such that the response's status code is a 404, the
test fails because the check_url() function doesn't handle
non-success responses how the test's assertions expect. This commit
updates check_url() to handle non-success responses, treating them
much like errors.

components/link_checker/src/lib.rs

@@ -71,7 +71,37 @@ pub fn check_url(url: &str, config: &LinkChecker) -> LinkResult {
                 Err(e) => LinkResult { code: None, error: Some(e.to_string()) },
             }
         }
-        Ok(response) => LinkResult { code: Some(response.status()), error: None },
+        Ok(response) => {
+            if response.status().is_success() {
+                LinkResult { code: Some(response.status()), error: None }
+            } else {
+                let error_string = if response.status().is_informational() {
+                    String::from(format!(
+                        "Informational status code ({}) received",
+                        response.status()
+                    ))
+                } else if response.status().is_redirection() {
+                    String::from(format!(
+                        "Redirection status code ({}) received",
+                        response.status()
+                    ))
+                } else if response.status().is_client_error() {
+                    String::from(format!(
+                        "Client error status code ({}) received",
+                        response.status()
+                    ))
+                } else if response.status().is_server_error() {
+                    String::from(format!(
+                        "Server error status code ({}) received",
+                        response.status()
+                    ))
+                } else {
+                    String::from("Non-success status code received")
+                };
+
+                LinkResult { code: None, error: Some(error_string) }
+            }
+        }
         Err(e) => LinkResult { code: None, error: Some(e.description().to_string()) },
     };