Change to follow kubeflow/common convention and reuse implementation

[Jeffwan]

Currently, mxnet operator API doesn't follow kubeflow/common convention and but controller does. It imports tf-operator implementation https://github.com/kubeflow/mxnet-operator/blob/c718707b304dc1ed0210a740c8efe7071d4ebb3e/pkg/controller.v1/mxnet/controller.go#L42

To graduate mxnet-operator to v1, we'd like to migrate to follow kubecom/common convention. It already has all the logic for ActiveDeadlineSeconds, BackoffLimit, etc. This will simplifies the implementation on mxnet-operator side.

[Jeffwan]

Working on a PR to address this issue

[Jeffwan]

/assign @Jeffwan