[SDK] test: add unit test for get_job method of the training_client

[Bobbins228]

What this PR does / why we need it:
add unit test for get_job method of the training_client

To verify run:

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

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

[coveralls]

Pull Request Test Coverage Report for Build 10698571584

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 7 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.04%) to 31.753%

---

Files with Coverage Reduction	New Missed Lines	%
pkg/controller.v1/mpi/mpijob.go	1	91.06%
pkg/controller.v1/mpi/mpijob_controller.go	6	80.67%

Totals
Change from base Build 10673563990:	-0.04%
Covered Lines:	3944
Relevant Lines:	12421

---

💛 - Coveralls

[andreyvelich]

@Bobbins228 Please rebase this PR

[andreyvelich]

Thank you for this @Bobbins228!
I left a few comments.

[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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[Bobbins228]

Thanks @andreyvelich I can take a look at some of the other UTs later in the week if we still have some that need to be written

[andreyvelich]

That sound great, we still have a few of them in this issue: #2161
Thanks for your contributions @Bobbins228!