Add terraform support for additional CIDR blocks.

[rdrgmnzs]

Add terraform support for additional CIDR blocks now that support has been added to terraform. The relevant terraform docs can be found at https://www.terraform.io/docs/providers/aws/r/vpc_ipv4_cidr_block_association.html

Follow up PR for #5270

[justinsb]

Thanks @rdrgmnzs

/approve
/lgtm

Do we want to cherry-pick this to 1.12?

The script I use is this one, BTW (you would git checkout -b release-1.12 then cherry 6693). But I'm also happy to do that!

#!/bin/bash -ex

set -o pipefail

PR=$1
BASE=`git rev-parse --abbrev-ref HEAD`

shas=`curl https://api.github.com/repos/kubernetes/kops/pulls/${PR}/commits  | jq -r .[].sha`

BRANCH="cherrypick_${PR}_${BASE}"

git checkout -b ${BRANCH}
for sha in $shas; do
 git cherry-pick $sha
done

git push ${USER}

cat <<EOF | hub pull-request -F - -b ${BASE}
Cherry pick of #${PR} onto ${BASE}

Cherry pick of #${PR}
EOF

git checkout ${BASE}

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: justinsb, rdrgmnzs

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[rdrgmnzs]

@justinsb since we're already looking at a kops 1.12-alpha.3 I say we should skip cherry picking this. It can just roll out in 1.13 when we have that as there's currently no open issues requesting it.