Allow CI tests to pass without external systems access

Currently the CI tests are a combination of external systems tests (which require external creds) and local tests which do not require creds. We should isolate the two types of tests, favoring those tests which can be run by anyone and either bifurcating or removing the others from the main suite of tests.

These tests were recently moved to separate subfolders in tests/ directory, with the tests/core representing those which do not require external creds. However, we do not yet favor those core tests one way or another, and we need to add a method to exclude other tests when running in local dev environments and on forked repos.