Add the pytorch-mnist with GPU support container image

[tenzen-y]

What this PR does / why we need it:
As discussed in this PR comments, I added the pytorch-mnist with GPU support container image and modified image name pytorch-mnist to pytorch-mnist-cpu.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Checklist:

• Docs included if any changes are user facing

[coveralls]

Coverage increased (+0.07%) to 73.068% when pulling 6d54642 on tenzen-y:add-pytorch-mnist-gpu-image into 8f182c2 on kubeflow:master.

[tenzen-y]

I have confirmed that Dockerfile is buildable in the following container images.

• https://hub.docker.com/r/ytenzen/katib-pytorch-mnist-cpu
• https://hub.docker.com/r/ytenzen/katib-pytorch-mnist-gpu

[tenzen-y]

/cc @johnugeorge @djmcgreal-cc

I will cherry-pick this PR for the release-0.14 branch after this PR is merged.

[google-oss-prow]

@tenzen-y: GitHub didn't allow me to request PR reviews from the following users: djmcgreal-cc.

Note that only kubeflow members and repo collaborators can review this PR, and authors cannot review their own PRs.

In response to this:

/cc @johnugeorge @djmcgreal-cc

I will cherry-pick this PR for the release-0.14 branch after this PR is merged.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[johnugeorge]

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: johnugeorge, tenzen-y

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