Add GPU support to minikube.

[rohitagarwal003]

Fixes #2115.

Testing this PR locally:

See the instructions added to docs/gpu.md in this PR. Even if you don't satisfy the prerequisites mentioned there, it would be useful to run these and check if the error messages returned are useful.

# From your minikube checkout
git fetch origin pull/2936/head:gpu-support
git checkout gpu-support

# Build the docker machine plugin
make out/docker-machine-driver-kvm2
cp out/docker-machine-driver-kvm2 /usr/local/bin/docker-machine-driver-kvm2

# Build minikube
make out/minikube

# Run minikube with GPUs
out/minikube start --vm-driver kvm2 --gpu --logtostderr

[rohitagarwal003]

/assign @vishh

[minikube-bot]

Can one of the admins verify this patch?

[vishh]

This PR overall lgtm. I'd recommend having some of the users wanting this feature in #2115 to try this out as well.

[vishh]

What would be the testing and maintenance story for this feature? If we need community help with maintenance, should we mark it as alpha/experimental until we can demonstrate sustained usage and maintenance?

[rohitagarwal003]

/assign @dlorenc @r2d4 @aaron-prindle

[rohitagarwal003]

This PR overall lgtm. I'd recommend having some of the users wanting this feature in #2115 to try this out as well.

Commented on that issue.

What would be the testing and maintenance story for this feature? If we need community help with maintenance, should we mark it as alpha/experimental until we can demonstrate sustained usage and maintenance?

The doc and help text say experimental. I would love to e2e test this but since GCE's nested virtualization doesn't have a virtual IOMMU, so we can't test this on GCE. If people have other ideas, I am all ears.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mindprince
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We suggest the following additional approver: aaron-prindle

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[dlorenc]

Thanks! The PR looks good to me. I'd like to think about the testing for another day or so and see if we can come up with something.

[rohitagarwal003]

Ping.

[dlorenc]

@minikube-bot OK to test