Make easier to disable exporting of environment with sudo

[willfurnass]

BatchSpawner fails on one of our Grid Engine clusters due to sudo being unable to export the environment (enabled by it's -E argument). We only allow certain environment variables to be exported - from our sudoers:

Defaults:jupyter env_keep+="SGE_ROOT SGE_CELL SGE_EXECD_PORT SGE_QMASTER_PORT SGE_CLUSTER_NAME LANG JPY_API_TOKEN"
jupyter        host1, host2 = (ALL) NOPASSWD: /usr/local/sge/live/bin/lx-amd64/qsub
jupyter        host1, host2 = (ALL) NOPASSWD: /usr/local/sge/live/bin/lx-amd64/qstat
jupyter        host1, host2 = (ALL) NOPASSWD: /usr/local/sge/live/bin/lx-amd64/qdel

To work around this issue I've added the following to our jupyterhub_config.py:

# Need to tailor use of sudo to ShARC as exporting of entire environment         
# using sudo's -E argument is not permitted here                                 
sudo_prefix = 'sudo -u {username} '                                              
c.GridengineSpawner.batch_submit_cmd = sudo_prefix + 'qsub'                      
c.GridengineSpawner.batch_query_cmd = sudo_prefix + 'qstat -xml'                 
c.GridengineSpawner.batch_cancel_cmd = sudo_prefix + 'qdel {job_id}' 

but do others think it would be nicer to have a neater way of setting this e.g. a can_sudo_export_env boolean trait?

[mbmilligan]

I'm not wild about having a boolean trait as you describe, since the current defaults are really intended as suggestions to administrators about how this can work, rather than reflecting a tight coupling to sudo. We've had people e.g. use ssh instead of sudo.

But, I think the logic in the config snippet you quote is right on the money, and we should have an exec_prefix configurable trait in the base class so that your use case only involves a one-line configuration change. Happy to accept a PR implementing that, although it'll probably wait until after we get a new release out.