[SDK] test: added unit tests for delete_job() method

[Bobbins228]

What this PR does / why we need it:
Added unit tests for the training_client.delete_job() method
Which issue(s) this PR fixes (optional, in Fixes #<issue number>, #<issue number>, ... format, will close the issue(s) when PR gets merged):
Ref #2161

Checklist:

• Docs included if any changes are user facing

[google-cla]

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[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[Bobbins228]

Hey @jinchihe,

Are you able to re-run the Google CLA check? It should work now :)

[terrytangyuan]

CLA check should not be here. https://github.com/kubeflow/community/blob/master/ksc/decision-log.md#switch-from-google-cla-to-dco

We are looking into this. cc @andreyvelich @james-jwu @zijianjoy

[andreyvelich]

@Bobbins228 We fixed the issue with Google CLA, please can you open a new PR with your change ?
Sorry for that!

[Bobbins228]

No worries @andreyvelich new PR incoming!