test: clear cleanup timer in tunnel tests

The cleanup timer wasn't cleared if a start/stop test was cancelled
which would make the self tests appear to hang.

Author: jason0x43

tests/support/integration.ts

@@ -142,12 +142,13 @@ export function addStartStopTest(
       }
 
       return tunnel
-        .start()!
+        .start()
         .then(function() {
           clearTimeout(cleanupTimer);
           return tunnel.stop();
         })
         .catch(reason => {
+          clearTimeout(cleanupTimer);
           if (reason.code === 'ECONNREFUSED') {
             this.skip('Service is unreachable');
           } else {