When operating e2e test, hack/e2e.go process creates kubetest process.
To kill the kubetest process when stop e2e test with Ctrl-C, we need
to send the signal to the process because it also creates another
process and it needs to kill it.
This PR adds the signal handler on hack/e2e.go to kill the kubetest
process.

NOTE: https://github.com/kubernetes/test-infra/pull/4154 is the part
      of kubetest.

solve #43051