failpoints: Add context to tool error message

We have a separate binary for setting failpoints, which works by
connecting to a Readyset controller instance.  If it fails, we now print
the status of what went wrong.

Also include instructions in the message telling the user how to compile
Readyset with support for failpoints.

Change-Id: Ibf5d9c7c689bae134e2b3a2f5b24fb051ab9db8a
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/8326
Reviewed-by: Jason Brown <[email protected]>
Tested-by: Buildkite CI

Author: davisjc

readyset-tools/src/failpoint.rs

@@ -49,7 +49,11 @@ impl Failpoint {
         let client = Client::new();
         let res = client.request(r).await.unwrap();
         let status = res.status();
-        assert!(status == hyper::StatusCode::OK);
+        assert!(
+            status == hyper::StatusCode::OK,
+            "status was: {} (don't forget to compile Readyset with --features failure_injection)",
+            status
+        );
         Ok(())
     }
 }