WIP: Plugin test suite

[mzanetti]

nymea:core pull request checklist:

Did you test the changes? If not (e.g. absence of required hardware), please mention a person to confirm it has been tested.

Did you update the documentation?

Did you update translations (cd builddir && make lupdate)?

[nymea-jenkins]

Refer to this link for build results (access rights to CI server needed): https://jenkins.nymea.io/job/nymea-pull-request-tester/1094/