Change default validation to openapi

[apelisse]

What this PR does / why we need it:
And also update the test to match the new error string.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes kubernetes/kubectl#49

Special notes for your reviewer:

Release note:

Performs validation (when applying for example) against OpenAPI schema rather than Swagger 1.0.

[mengqiy]

/lgtm

[apelisse]

/retest

[k8s-github-robot]

Adding do-not-merge/release-note-label-needed because the release note process has not been followed.
One of the following labels is required "release-note", "release-note-action-required", "release-note-experimental" or "release-note-none".
Please see: https://github.com/kubernetes/community/blob/master/contributors/devel/pull-requests.md#write-release-notes-if-needed.

[apelisse]

@mengqiy @pwittrock PTAL

[mengqiy]

/lgtm

[apelisse]

/retest

[pwittrock]

/approve kubernetes/kubect#49

[k8s-github-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: apelisse, mengqiy, pwittrock

Associated issue: 49

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these OWNERS Files:

• hack/OWNERS [pwittrock]
• pkg/kubectl/OWNERS [pwittrock]

You can indicate your approval by writing /approve in a comment
You can cancel your approval by writing /approve cancel in a comment

[CaoShuFeng]

/test pull-kubernetes-verify

[fejta-bot]

/retest
This bot automatically retries jobs that failed/flaked on approved PRs (send feedback to @fejta).

Review the full test history for this PR.

[k8s-github-robot]

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

[k8s-github-robot]

Automatic merge from submit-queue (batch tested with PRs 51335, 51364, 51130, 48075, 50920)

[k8s-ci-robot]

@apelisse: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
pull-kubernetes-e2e-kops-aws	9287eb0	link	/test pull-kubernetes-e2e-kops-aws

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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. I understand the commands that are listed here.