Errors in coroutines on closing a `KubeCluster` that was never entered/started

[ig248]

Steps to reproduce

PYTHONASYNCIODEBUG=1 python -c "from dask_kubernetes import KubeCluster; KubeCluster()"

shows a number of errors.

Update - fairly low priority in retrospect

this is due to no pod_template being provided. The error handling is happening in a coroutine - should it be made to fail synchronously for easier debugging?

[jacobtomlinson]

The classic KubeCluster was removed in #890. All users will need to migrate to the Dask Operator. Closing.