Helm chart: write a test

Helm chart as it is now, and as it will be needs a test, that it still deploys all components, and that they work.

Acceptance criteria:

• develop a test, that will install Mender of given version via Helm chart
• include in the CI pipeline
  • install tiller, helm, minikube
  • deploy mender
  • create tenant
  • create user
  • login