Support different remote_python paths on cluster nodes

[abduhbm]

Trying to resolve #4063

cluster = SSHCluster(["hostA", "hostA", "hostB"], 
                     remote_python={'hostA': '/tmp/condaA/bin/python', 
                                    'hostB': '/tmp/condaB/bin/python'}, 
                     connect_options={"known_hosts": None},
                     worker_options={"nthreads": 2},
                     scheduler_options={"port": 0, "dashboard_address": ":8797"})

> w = cluster.workers
> w[0].remote_python
/tmp/condaA/bin/python
> w[1].remote_python
/tmp/condaB/bin/python

@jacobtomlinson please let me know if more work is needed here. Thanks,

[abduhbm]

@jacobtomlinson I would appreciate your feedback on this.

[jacobtomlinson]

Thanks for this @abduhbm.

My main comment here is other options take either a single option or a list of options. So for connect_options it can either be a dictionary of settings which are applied to all connections, or a list of dictionaries.

The list length must match the order and length of the addresses list.

I would suggest this should follow the same pattern.

[abduhbm]

@jacobtomlinson thanks for the feedback.
remote_python now accepts str or list of str.

[jacobtomlinson]

This looks great thanks

[mrocklin]

My apologies for the delay. @jacobtomlinson thank you for the review.

I'm merging this in. Thanks @abduhbm !