SDK - Containers - Do not create GCS bucket unless building the image

[Ark-kun]

Previously, when the user tried to construct ContainerBuilder it immediately created a storage bucket even is no image was build. This prevented the creation of default builder instance.

Also missing default image name is no longer an error as long as the image name is provided to ContainerBuilder.build.

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This change is 

[Ark-kun]

/retest

[Ark-kun]

@numerology I've talked to @gaoning777 and he agreed with the idea of this refactoring.

[numerology]

/lgtm

Left one nit comment.

[gaoning777]

@numerology I've talked to @gaoning777 and he agreed with the idea of this refactoring.

Just for the record, I'm not strongly opinionated about whether fetching the project id/creating bucket in the constructor or in the build function.
However, this refactoring does change the constructor signature(default_image_name). I understand that this class is not exposed in the init.py but there might still be users using it. I'm suggesting to not break that change.

[Ark-kun]

However, this refactoring does change the constructor signature(default_image_name). I understand that this class is not exposed in the init.py but there might still be users using it. I'm suggesting to not break that change.

Sure. I'll split that change out.

[Ark-kun]

However, this refactoring does change the constructor signature(default_image_name).

Changed that back. @gaoning777

[gaoning777]

/lgtm

[Ark-kun]

/approve
/retest

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[Ark-kun]

/test kubeflow-pipeline-sample-test

[Ark-kun]

/test kubeflow-pipeline-sample-test

[gaoning777]

Do you want to merge with master? Looks like the samples tests are failing consistently.

[Ark-kun]

Do you want to merge with master? Looks like the samples tests are failing consistently.

I've checked and these were temporary issues with PyPI network.