Add ability for checking connection to kubernetes cluster.

I got the error: Something went wrong while installing Helm Tiller when trying to install helm. I tried to get logs from the pod but didn't get pods. Then I changed the CA certificate and gitlab was success save it. When I tried to install helm I got the same error: Something went wrong while installing Helm Tiller. Most likely, gitlab can't connect to the cluster, but check it impossible. I propose to add a button which should run a process that will try to connect to the cluster and get its information.