Add e2e test for the component build(use multiple output sample)

[gaoning777]

This issue is to track adding a sample test for the component build(func_to_containerop).
Currently we have a sample https://github.com/kubeflow/pipelines/tree/master/samples/core/multiple_outputs, which uses the build_python_component function. We can convert it to use the new func_to_containerop and add the test to the e2e.

[gaoning777]

This sample as well: https://github.com/kubeflow/pipelines/tree/master/samples/core/component_build

[gaoning777]

#1813

[gaoning777]

multiple_output sample is not tested, yet

[Ark-kun]

multiple_output sample is not tested, yet

Tracking that in #2208
Also #2209 #2210

[gaoning777]

Is the func_to_container_op conversion necessary for the tests?
Or we could add the tests and then convert?

[Ark-kun]

Is the func_to_container_op conversion necessary for the tests?

It's not necessary. I was just going with what you put in the description of this issue: "We can convert it to use the new func_to_containerop and add the test to the e2e.".

[gaoning777]

SGTM. Let's add the test first then.

[Ark-kun]

@gaoning777 Should we close this issue since both samples are now covered by sample tests?