fix api reader issue

[zw0610]

What this PR does / why we need it:

Function GetJobFromAPIClient is used to get the kubeflow Job from APIServer directly without cache. However, the contemporary implementation is hard to understand and will panic when CacheReader is called: https://github.com/kubernetes-sigs/controller-runtime/blob/master/pkg/client/split.go#L130

The Manager in controller-runtime offers APIReader which does the work to get job from APIServer.

This PR changes how GetJobFromAPIClient to get job from APIServer by adding APIReader to Reconcilers.

[zw0610]

/hold for more comment

[coveralls]

Pull Request Test Coverage Report for Build 2003571271

• 15 of 30 (50.0%) changed or added relevant lines in 5 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.1%) to 36.921%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/controller.v1/mpi/mpijob_controller.go	5	6	83.33%
pkg/controller.v1/pytorch/pytorchjob_controller.go	5	6	83.33%
pkg/controller.v1/tensorflow/tfjob_controller.go	5	6	83.33%
pkg/controller.v1/mxnet/mxjob_controller.go	0	6	0.0%
pkg/controller.v1/xgboost/xgboostjob_controller.go	0	6	0.0%

Files with Coverage Reduction	New Missed Lines	%
pkg/controller.v1/mpi/mpijob_controller.go	2	75.35%

Totals
Change from base Build 1996927612:	0.1%
Covered Lines:	2278
Relevant Lines:	6170

---

💛 - Coveralls

[cheimu]

That's awesome! After this pr is merged, the MPIJob panic bug when GetJobFromAPIClient could be solved!

[terrytangyuan]

Thanks!

/lgtm
/approve

[Jeffwan]

Reuse APIReader from manager makes more sense.

/lgtm

[gaocegege]

/lgtm

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gaocegege, Jeffwan, terrytangyuan, zw0610

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

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [Jeffwan,gaocegege,terrytangyuan,zw0610]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[zw0610]

/unhold