Update Z-Wave Tests asyncio/yield from -> async/await

[cgarwood]

Description:

Updates Z-Wave tests to use the async/await syntax instead of asyncio.coroutine and yield from

Related issue (if applicable): N/A

Pull request in home-assistant.io with documentation (if applicable): N/A

Example entry for configuration.yaml (if applicable):

zwave:

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.

[balloob]

Ok to merge when CI passes