Run kubectl in all/some contexts (clusters) in parallel

Allow you to run kubectl command in multiple contexts (clusters) in parallel, like this

$ kubectl allctx /-prod/ minikube -- get pods -n kube-system --selector compute.twitter.com/app=coredns --no-headers

     eu-prod | coredns-59bd9867bb-6rbx7   2/2     Running   0          78d
     eu-prod | coredns-59bd9867bb-9xczh   2/2     Running   0          78d
     eu-prod | coredns-59bd9867bb-fvn6t   2/2     Running   0          78d
    minikube | No resources found in kube-system namespace.
 useast-prod | coredns-6fd4bd9db4-7w9wv   2/2     Running   0          78d
 useast-prod | coredns-6fd4bd9db4-9pk8n   2/2     Running   0          78d
 useast-prod | coredns-6fd4bd9db4-xphr4   2/2     Running   0          78d
 uswest-prod | coredns-6f987df9bc-6fgc2   2/2     Running   0          78d
 uswest-prod | coredns-6f987df9bc-9gxvt   2/2     Running   0          78d
 uswest-prod | coredns-6f987df9bc-d88jk   2/2     Running   0          78d