Remove direct visibility constraints for nodes in a cluster

[jumutc]

For a heterogeneous clusters where nodes are visible to each other only via the ssh tunnelling it would be nice to have a workaround for making addprocs routine working in this case.

Please consider another issue #6256 which explained the problem and resulted in the necessity of a feature request.

[jumutc]

Please consider my implementation of this feature: #6277.
I have some doubts still regarding the proper name for the option in addprocs which one can use to indicate that the tunnel between workers (nodes) is needed. I have checked #6277 against my case and a homogeneous cluster.

[jumutc]

Could anyone evaluate my fix to this problem: #6277?

[pao]

cc @amitmurthy (who is assigned, but GitHub doesn't tell me who changed that, so no idea if he's aware.)

[aviks]

I think Amit mentioned on another issue that he's going to be away for a bit

[jumutc]

@amitmurthy: is #6277 rejected?

[amitmurthy]

Feature best done in an external ClusterManager and possibly added to ClusterManagers.jl