Announce environmental overrides up front

[tstromberg]

This helps to address issues like #5207 where the user has forgotten or is not aware of what environment variables may have been previously set. Example run:

😄  minikube v1.3.1 on Darwin 10.14.6
    ▪ MINIKUBE_HOME=/tmp
    ▪ KUBECONFIG=/tmp/.kc
💡  Tip: Use 'minikube start -p <name>' to create a new cluster, or 'minikube delete' to delete this one.
🔄  Starting existing virtualbox VM for "minikube" ...
⌛  Waiting for the host to be provisioned ...

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[afbjorklund]

Sounds good to me, I guess we have no secrets in environment variables (would we) ?

[tstromberg]

Sounds good to me, I guess we have no secrets in environment variables (would we) ?

Not yet! If we ever do, we can mask it.