Improve testing harness to allow tests on real devices (#197)

* test_cli: provide return values to patched objects to avoid warning about non-awaited calls

* test_cli: restore alias after testing

* smartstrip: remove internal update() calls for turn_{on,off}, set_led

* Make sure power is always a float

* Fix discovery tests

* Make tests runnable on real devices

* Add a note about running tests on a real device

* test_strip: run update against the parent device

pyproject.toml

@@ -72,6 +72,11 @@ fail-under = 100
 exclude = ['kasa/tests/*']
 verbose = 2
 
+[tool.pytest.ini_options]
+markers = [
+    "requires_dummy: test requires dummy data to pass, skipped on real devices",
+]
+
 [build-system]
 requires = ["poetry>=0.12"]
 build-backend = "poetry.masonry.api"