E2E tests creating objects with gcloud

[nachocano]

Problem
Our e2e tests currently create the resources using the client-go. However, many users will be inclined to use gcloud. The experience there is to create a Trigger, which in turn will create a Source and hook them together.
We've seen problems because of gcloud sending nil values as empty, unkown fields, etc.
We should have e2e tests that create things using gcloud.

Persona:
Contributor

Exit Criteria
E2E tests that use gcloud to create objects

Time Estimate (optional):
?

[nachocano]

/cc @chizhg
/cc @nlopezgi keep this one in mind while you do the refactor. We will probably need a "configurable" creation step, and then reuse all the same tests...

[nachocano]

We should also test the reply mechanism as part of these tests

[nachocano]

Moving to v1beta1 seems that it might break gcloud. We need to make sure we are not.

[nlopezgi]

@danyinggu will start looking at this issue

[grantr]

Great thanks @danyinggu!

/assign @danyinggu

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In response to this:

Great thanks @danyinggu!

/assign @danyinggu

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[ericlem]

We're going to test this elsewhere.