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

kasa/tests/test_emeter.py

@@ -32,6 +32,7 @@ async def test_get_emeter_realtime(dev):
 
 
 @has_emeter
+@pytest.mark.requires_dummy
 async def test_get_emeter_daily(dev):
     if dev.is_strip:
         pytest.skip("Disabled for strips temporarily")
@@ -54,6 +55,7 @@ async def test_get_emeter_daily(dev):
 
 
 @has_emeter
+@pytest.mark.requires_dummy
 async def test_get_emeter_monthly(dev):
     if dev.is_strip:
         pytest.skip("Disabled for strips temporarily")