[k8s] docker could error out more clearly when there is no kubernetes configuration file

[vdemeester]

When kubernetes is use as the orchestrator but there is not $HOME/.kube/config, the docker cli errors out without too much context.

$ docker stack deploy -c docker-compose.yml foo
Failed to load kubernetes configuration file '/home/vincent/.kube/config'

We may want to add more context on the error, like why we're looking at that file, etc..

cc @thaJeztah @silvin-lubecki

[olljanat]

@vdemeester this one looks to be fixed?

[thaJeztah]

Yes, looks like this was fixed through #1216