CI: Extend integration testing

Refactor the integration test script to support running a variety of tests, and add CI jobs for them.

We might want to combine some of these jobs, or otherwise adjust things, but this was minimal effort to add and should improve our test coverage a bit.

pmb/parse/deviceinfo.py

@@ -35,6 +35,13 @@ def _parse_kernel_suffix(info, device, kernel):
                "b": "second",
                "b_downstream": "third"}
     """
+    # We don't support parsing the kernel variants in tests yet, since this code
+    # depends on pmaports being available and calls into a whole lot of other code.
+    if os.environ.get("PYTEST_CURRENT_TEST", "").startswith("pmb/parse/test_deviceinfo.py"):
+        # If you hit this, you're probably trying to add a test for kernel variants.
+        # You'll need to figure out how to mock the APKBUILD parsing below.
+        assert kernel is None
+        return info
     # Do nothing if the configured kernel isn't available in the kernel (e.g.
     # after switching from device with multiple kernels to device with only one
     # kernel)