@Link39 Z-Wave PR with fixes and tests

[Pierre-Gilles]

Pull Request check-list

To ensure your Pull Request can be accepted as fast as possible, make sure to review and check all of these items:

• If your changes affects code, did your write the tests?
• Are tests passing? (npm test on both front/server)
• Is the linter passing? (npm run eslint on both front/server)
• Did you run prettier? (npm run prettier on both front/server)
• If you are adding a new features/services, did you run integration comparator? (npm run compare-translations on front)
• If your changes modify the API (REST or Node.js), did you modify the API documentation? (Documentation is based on comments in code)
• If you are adding a new features/services which needs explanation, did you modify the user documentation? See the GitHub repo and the website.
• Did you add fake requests data for the demo mode (front/src/config/demo.json) so that the demo website is working without a backend? (if needed) See https://demo.gladysassistant.com.

NOTE: these things are not required to open a PR and can be done afterwards / while the PR is open.

Description of change

Please provide a description of the change here. It's always best with screenshots, so don't hesitate to add some!

[codecov]

Codecov Report

Merging #893 into master will increase coverage by 0.04%.
The diff coverage is 96.87%.

@@            Coverage Diff             @@
##           master     #893      +/-   ##
==========================================
+ Coverage   93.53%   93.58%   +0.04%     
==========================================
  Files         461      461              
  Lines        6112     6123      +11     
==========================================
+ Hits         5717     5730      +13     
+ Misses        395      393       -2     

Impacted Files	Coverage Δ
server/services/zwave/lib/constants.js	100.00% <ø> (ø)
server/services/zwave/lib/utils/getCategory.js	100.00% <ø> (ø)
server/utils/constants.js	100.00% <ø> (ø)
...er/services/zwave/lib/events/zwave.valueRemoved.js	80.00% <66.66%> (-20.00%)	⬇️
...rver/services/zwave/lib/commands/zwave.getNodes.js	96.42% <100.00%> (+0.42%)	⬆️
...rver/services/zwave/lib/events/zwave.valueAdded.js	100.00% <100.00%> (ø)
...er/services/zwave/lib/events/zwave.valueChanged.js	100.00% <100.00%> (ø)
server/services/zwave/lib/utils/getUnit.js	100.00% <100.00%> (+37.50%)	⬆️

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