Improve cronjob concurrency policy doc

[tengqm]

What this PR does / why we need it:
The CronJob API documentation (https://kubernetes.io/docs/api-reference/v1.8/#cronjobspec-v1beta1-batch) did not clearly state what can be used as concurrencyPolicy. Instead, it only says that the default value is "Raw".

Which issue(s) this PR fixes:

Special notes for your reviewer:
This patch is not changing any code logic but it involves generated "code".

Release note:

NONE

[k8s-ci-robot]

Hi @tengqm. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

I understand the commands that are listed here.

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.

[k82cn]

/ok-to-test

[tengqm]

/retest pull-kubernetes-unit

[tengqm]

/test pull-kubernetes-unit

[tengqm]

/assign @smarterclayton

[smarterclayton]

/approve no-issue
/lgtm

Thanks for the cleanup

[k8s-github-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: smarterclayton, tengqm

Associated issue requirement bypassed by: smarterclayton

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

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

• api/OWNERS [smarterclayton]
• docs/api-reference/OWNERS [smarterclayton]
• pkg/apis/OWNERS [smarterclayton]
• staging/src/k8s.io/api/OWNERS [smarterclayton]

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

[k8s-github-robot]

/test all

Tests are more than 96 hours old. Re-running tests.

[tengqm]

/test pull-kubernetes-node-e2e

[k8s-github-robot]

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

[k8s-github-robot]

/test all

Tests are more than 96 hours old. Re-running tests.

[k8s-github-robot]

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions here.