adds e2e-layering test package

[cheesesashimi]

- What I did

I've added an empty e2e-layering test package which is intended to house future tests related to the OpenShift CoreOS Layering effort as well as an additional Makefile target.

- How to verify it

1. Clone this PR.
2. $ make test-e2e-layering

- Description for the changelog
Enables e2e layering tests

[cheesesashimi]

/hold

[cheesesashimi]

/unhold

[kikisdeliveryservice]

/lgtm

[cgwalters]

/approve
/skip

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cgwalters, cheesesashimi, kikisdeliveryservice

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• OWNERS [cgwalters,kikisdeliveryservice]

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[openshift-ci]

@cheesesashimi: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/e2e-gcp-single-node	dabe2ee	link	false	/test e2e-gcp-single-node

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