Customize kubeconfig to use different clustername and user

[bplein]

I propose that the Kubeconfig generated by px-deploy kubeconfig should change the clusterName from kubernetes to the name of that cluster (examples: myCluster or in a multiple cluster deployment, myCluster.1, 'MyCluster.2

In addtion, to save space for those using command prompts that include the kubernetes context, change the user from kubernetes-admin to just admin

We should do this for the master config file as well.