There's no current support for automatically aborting/canceling builds; I don't remember a real request for this behavior (Locally, I've had users ask for it, but the need was driven from an artificially-limited build resources; Once that limit was fixed, the requests were gone).

There's no current support for sending an HTTP request for canceling a remote job; I've started writing it (D15958), but it's no longer a priority for me either. I'm not sure that it actually fits your request - maybe you want to invoke specific "build steps" as "cancel build" instead. It's also more intended for custom build steps, rather then the built-in "HTTP Request" step.