Usability: check addon status before disable.

[fenglixa]

Usability issue. While disable an addon, should message to user the addon is not enabled, but not a disabled failed crash message as below:

The exact command to reproduce the issue:
minikube addons disable heapster

The full output of the command that failed:
✘ > ~/Documents/GitHub/minikube_fengli > > master > minikube addons disable heapster
✅ heapster was successfully disabled
~/Documents/GitHub/minikube_fengli > > master > minikube addons disable heapster

💣 disable failed: [disabling addon deploy/addons/heapster/influx-grafana-rc.yaml.tmpl: Process exited with status 1]
😿 Sorry that minikube crashed. If this was unexpected, we would love to hear from you:
👉 https://github.com/kubernetes/minikube/issues/new

The output of the minikube logs command:

✘ > ~/Documents/GitHub/minikube_fengli > > master > minikube logs |tail
2019/06/03 13:28:04 Metric client health check failed: the server is currently unable to handle the request (get services heapster). Retrying in 30 seconds.
2019/06/03 13:28:34 Metric client health check failed: the server is currently unable to handle the request (get services heapster). Retrying in 30 seconds.
2019/06/03 13:29:04 Metric client health check failed: the server is currently unable to handle the request (get services heapster). Retrying in 30 seconds.
2019/06/03 13:29:34 Metric client health check failed: the server is currently unable to handle the request (get services heapster). Retrying in 30 seconds.
2019/06/03 13:30:04 Metric client health check failed: the server is currently unable to handle the request (get services heapster). Retrying in 30 seconds.
2019/06/03 13:30:34 Metric client health check failed: the server is currently unable to handle the request (get services heapster). Retrying in 30 seconds.
2019/06/03 13:31:04 Metric client health check failed: the server is currently unable to handle the request (get services heapster). Retrying in 30 seconds.
2019/06/03 13:31:34 Metric client health check failed: the server is currently unable to handle the request (get services heapster). Retrying in 30 seconds.

==> storage-provisioner <==

The operating system version:
MAC OS

[dpandhi-git]

would like to work on it