xgb yaml container name should be consistent with xgb job default container name

[Crisescode]

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in Fixes #<issue number>, #<issue number>, ... format, will close the issue(s) when PR gets merged):
Fixes #

Checklist:

• Docs included if any changes are user facing

[coveralls]

Pull Request Test Coverage Report for Build 4778027694

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 39.338%

---

Files with Coverage Reduction	New Missed Lines	%
pkg/controller.v1/mpi/mpijob_controller.go	2	76.79%

Totals
Change from base Build 4659763896:	-0.1%
Covered Lines:	2732
Relevant Lines:	6945

---

💛 - Coveralls

[tenzen-y]

Thank you! We must use the xgboost as a default container name.

training-operator/pkg/apis/kubeflow.org/v1/xgboost_types.go

Lines 28 to 29 in 8a066f9

	// XGBoostJobDefaultContainerName is the name of the XGBoostJob container.
	XGBoostJobDefaultContainerName = "xgboost"

/lgtm
/assign @terrytangyuan @johnugeorge @gaocegege

[tenzen-y]

ping :) > @terrytangyuan @johnugeorge @gaocegege

[johnugeorge]

Sorry. I missed it

/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Crisescode, johnugeorge

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 [johnugeorge]

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