none UX: Reword warnings and other strings for accuracy

[tstromberg]

Minor display fixes I noticed while battle-testing minikube with the none driver:

• Remove kubectl download guidance when minikube is run without kubectl in path, as is often the case when run as root. The installation guidance provided conflicted with the offficial instructions anyways.
• The giant none warning was no longer accurate. Linked to doc for more information.
• Make chown command work when there is no group named $USER
• The dashboard will now exit much earlier if kubectl is missing.
• Log an error if the bootstrapper can't be initialized
• Some mentions of VM should actually be cluster, particularly when used with none.

Sample output:

😄  minikube v0.33.1 on linux (amd64)
🤹  Configuring local host environment ...

⚠️  The 'none' driver provides limited isolation and may reduce system security and reliability.
⚠️  For more information, see:
👉  https://github.com/kubernetes/minikube/blob/master/docs/vmdriver-none.md

⚠️  kubectl and minikube configuration will be stored in /root
⚠️  To use kubectl or minikube commands as your own user, you may
⚠️  need to relocate them. For example, to overwrite your own settings:

    ▪ sudo mv /root/.kube /root/.minikube $HOME
    ▪ sudo chown -R $USER $HOME/.kube $HOME/.minikube

💡  This can also be done automatically by setting the env var CHANGE_MINIKUBE_NONE_USER=true
💡  Tip: To create a new cluster, use 'minikube start -p <new name>' or use 'minikube delete' to delete this one.
🏃  Re-using the currently running none VM for "minikube" ...
⌛  Waiting for SSH access ...
📶  "minikube" IP address is 172.31.148.205
🐳  Configuring Docker as your container runtime ...
✨  Preparing Kubernetes environment ...
🚜  Pulling images used by Kubernetes v1.13.3 ...
🔄  Relaunching Kubernetes v1.13.3 using kubeadm ... 
⌛  Restarting kube-proxy ...

This resolves #3429 and #3263

[k8s-ci-robot]

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This pull-request has been approved by: tstromberg

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[tstromberg]

@minikube-bot OK to test