Z2m clean code

[atrovato]

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)
• [ ] Did you test this pull request in real life? With real devices? If this development is a big feature or a new service, we recommend that you provide a Docker image to the community for testing before merging.
• [ ] 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.js) 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[bot]]

Codecov Report

Merging #64 (f0bce83) into master (825c4e2) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #64   +/-   ##
=======================================
  Coverage   96.81%   96.81%           
=======================================
  Files         660      662    +2     
  Lines        9628     9647   +19     
=======================================
+ Hits         9321     9340   +19     
  Misses        307      307           

Impacted Files	Coverage Δ
server/services/zigbee2mqtt/lib/constants.js	100.00% <ø> (ø)
server/lib/system/system.getGladysContainerId.js	100.00% <100.00%> (ø)
...services/zigbee2mqtt/api/zigbee2mqtt.controller.js	100.00% <100.00%> (ø)
server/services/zigbee2mqtt/lib/connect.js	100.00% <100.00%> (ø)
server/services/zigbee2mqtt/lib/disconnect.js	100.00% <100.00%> (ø)
...erver/services/zigbee2mqtt/lib/getConfiguration.js	100.00% <100.00%> (ø)
...rver/services/zigbee2mqtt/lib/handleMqttMessage.js	100.00% <100.00%> (ø)
server/services/zigbee2mqtt/lib/index.js	100.00% <100.00%> (ø)
server/services/zigbee2mqtt/lib/init.js	100.00% <100.00%> (ø)
...r/services/zigbee2mqtt/lib/installMqttContainer.js	100.00% <100.00%> (ø)
... and 5 more

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.