tests: setup CI for end to end tests

[diegodelemos]

Get a Kubernetes cluster running on CI environment with service account token (needed by REANA-Job-Controller) and test that examples work using reana CLI (reana install-client, reana install-cluster, reana run-example...). Some known options:

• Use GitLab Kubernetes integration, https://edenmal.moe/post/2018/GitLab-Kubernetes-Using-GitLab-CIs-Kubernetes-Cluster-feature/
  PROs:
  testing on the same environment as production (real Kubernetes cluster)
• Minikube without VMs
  PROs:
  Well-known behavior
  Supports StorageClass out of the box, i.e. can use Kubernetes' PVs
• Mirantis kubeadm-dind-cluster
  PROs:
  As the Kubernetes cluster is created with multiple "nodes" (implemented as Docker containers in the running host), it's possible to stage affinity setups and run operations like node drain, cordon, etc

[diegodelemos]

So far I could partially configure the first option with CERN Gitlab. I connected GitLab CI with a running magnum managed Kubernetes cluster but didn't use it in a pipeline yet.