Debian Stretch versions for Docker to support K8s 1.8

[mikn]

Sadly no armhf support, as Docker only started building armhf builds for 17.06+ for Debian Stretch.
This fixes #2783

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[chrislovecnm]

/ok-to-test

pending on check with @justinsb for LGTM otherwise it does LGTM

[justinsb]

/lgtm

Thanks @mikn

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: justinsb

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[k8s-github-robot]

/test all [submit-queue is verifying that this PR is safe to merge]

[k8s-github-robot]

Automatic merge from submit-queue.

[mikn]

@justinsb Happy to help!