Duplicated propertyStatus messages on /things websocket

[cdelston0]

I see duplicated propertyStatus messages on the /things websocket interface when native webthing properties change.

This can be reproduced with the test code at: https://github.com/cdelston0/gateway-test

Steps to reproduce:

• start gateway and ensure that native webthings addon is enabled.
• run test case MultipleThingProfiling.test_5_property_change_at_webthing

e.g.:
python3 test.py --gateway-url=http://localhost:8080/ --gateway-user=testuser@email.com --gateway-password=testpass MultipleThingProfiling.test_5_property_change_at_webthing

Output of the form:

http---laptop.local-8800 sequence correct: False
http---laptop.local-8800 sequence was: [1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10]

... indicates repeated propertyStatus websocket messages were received.

Note that this doesn't occur every time the test case is run, and you may need to run multiple times to exhibit the behaviour. Once it has started to happen, it seems like it will continue to do so.

The gateway log will contain output like:

2019-12-12 17:11:07.256 INFO : thing-url: getValue for property idx for: a testThing on port 8800 returning 8
2019-12-12 17:11:07.256 INFO : thing-url: getValue for property idx for: a testThing on port 8800 returning 8
2019-12-12 17:11:12.262 INFO : thing-url: getValue for property idx for: a testThing on port 8801 returning 8
2019-12-12 17:11:12.262 INFO : thing-url: getValue for property idx for: a testThing on port 8801 returning 8
2019-12-12 17:11:17.265 INFO : thing-url: getValue for property idx for: a testThing on port 8802 returning 8
2019-12-12 17:11:17.266 INFO : thing-url: getValue for property idx for: a testThing on port 8802 returning 8
2019-12-12 17:11:22.273 INFO : thing-url: getValue for property idx for: a testThing on port 8803 returning 8
2019-12-12 17:11:22.274 INFO : thing-url: getValue for property idx for: a testThing on port 8803 returning 8
2019-12-12 17:11:27.279 INFO : thing-url: getValue for property idx for: a testThing on port 8804 returning 8
2019-12-12 17:11:27.280 INFO : thing-url: getValue for property idx for: a testThing on port 8804 returning 8
2019-12-12 17:11:32.287 INFO : thing-url: getValue for property idx for: a testThing on port 8800 returning 9
2019-12-12 17:11:32.287 INFO : thing-url: getValue for property idx for: a testThing on port 8800 returning 9

[cdelston0]

WebThingsIO/thing-url-adapter#84 Fixes this for me.