Make installer more robust (platform AKS)

[roman-ferstl]

We ran into the issue that "keptn install" failed on AKS as we did not perform "az login" beforehand. We then had corrupt configurations for kubectl and keptn cli resulting in errors on each retry of keptn-install. Our solution was to make a new connection manually via:
az aks get-credentials --resource-group myResourceGroup --name myAKSCluster
Note that the errors occured on the client side before reaching the AKS instance.

Maybe a "keptn reset" command or a sanity check before the actual installation is peformed would help already.

[roman-ferstl]

opened under: keptn/keptn#1927