techdebt: Regression tests --> system tests

[ryanseys]

Technically our "regression tests" are really integration system tests. Adding this issue as a technical debt so that maybe someday we will get around to renaming it in the various places.

[dhermes]

👍 /cc @tseaver

[tseaver]

I'd really prefer "functional" or "system" to "integration" for the gcloud-python ones: they are end-to-end tests of the whole system, rather than tests of integrated assemblies of components.

[ryanseys]

Agreed. +1 for system tests.