Initial implementation of kubectl command

[afbjorklund]

Some duplication, always using default k8s

For #3645

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[tstromberg]

The implementation here seems sound, but after reviewing our uses of kubectl, I'm left wondering if this command is worth the technical debt it incurs. I feel that if users want to use kubectl, they may as well install it properly so that they may use it for a non-minikube cluster.

Thoughts?

[afbjorklund]

As long as kubectl is just a Recommends in a .deb so that it gets automatically pulled with the sudo apt install minikube (which would of course also install needed drivers as Depends), then everything is fine...

But after putting the poor user through:
https://kubernetes.io/docs/tasks/tools/install-minikube/#linux

curl -Lo minikube https://storage.googleapis.com/minikube/releases/latest/minikube-linux-amd64
chmod +x minikube
sudo cp minikube /usr/local/bin && rm minikube

The last thing to do is making them do:
https://kubernetes.io/docs/tasks/tools/install-kubectl/#install-kubectl-binary-using-curl

curl -LO https://storage.googleapis.com/kubernetes-release/release/v1.13.0/bin/linux/amd64/kubectl
chmod +x ./kubectl
sudo mv ./kubectl /usr/local/bin/kubectl

Where it "forgets" to use the checksums, and is prone to using the wrong version of kubectl. The only difference between this and "properly", seems to be the extra step of copying it along the $PATH ?

---

To be honest I am not sure why we require the user to have sudo rights ?
They would probably be just as well off, by copying them to ~/.local/bin

I've also seen at least a dozen different ways to do the above, with chown etc.
Even these two pages in the Kubernetes docs also vary, ever so slightly.

[afbjorklund]

This command can use the new machine.CacheBinary function instead, once #3737 is merged.

[tstromberg]

@minikube-bot OK to test

[tstromberg]

This seems ready to merge once we have positive test results.

[tstromberg]

Please rebase and merge once ready. Thanks!

[afbjorklund]

Will wait for 1.1

[tstromberg]

@minikube-bot OK to test