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

[Bobbins228]

What this PR does / why we need it:
add unit tests for 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

To verify run:

pytest -v sdk/python/kubeflow/training/api/training_client_test.py -k test_delete_job

Checklist:

• Docs included if any changes are user facing

[Bobbins228]

New PR created following conversation in #2202

[andreyvelich]

/ok-to-test
/rerun-all

[andreyvelich]

Please rebase your PR @Bobbins228.

[Bobbins228]

@andreyvelich both PRs are updated 👍

[andreyvelich]

@bhupc I think, we need one more rebase since we recently push changes to the training client tests.

[coveralls]

Pull Request Test Coverage Report for Build 10667942572

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 31.793%

---

Files with Coverage Reduction	New Missed Lines	%
pkg/controller.v1/mpi/mpijob_controller.go	2	81.05%

Totals
Change from base Build 10639523457:	-0.02%
Covered Lines:	3949
Relevant Lines:	12421

---

💛 - Coveralls

[Bobbins228]

@andreyvelich rebased

[andreyvelich]

Thanks for the update @Bobbins228!
Just a few comments from me.

[andreyvelich]

Thanks for the update @Bobbins228!
/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andreyvelich

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