Implement a cluster status method, to know if workers are really running

Currently, we only know that we have submitted some jobs to a cluster scheduler. We don't know if these jobs are running or queued, or in any other state.

What do you think of implementing a kind of status method?

In the PBS case for example, it would issue a qstat call, and get the PBS scheduler status of every jobs handled by the Dask cluster.

Not sure if this is really needed, as we are able with the use of Dask Client to know the real size of the cluster (and maybe by some other means).

Maybe this issue is just about documenting how to retrieve the information about a cluster state, either by job scheduler (eg. PBS) API, either using Dask API.