Prevent rewriting the slurm-remote-host variable to use the extension without an explicit tramp connection

[aancel]

Hello,

Following the discussion on #8, this PR prevents rewriting the slurm-remote-host variable, thus it should enable the following workflow:

• Set the slurm-remote-host variable
• M-x slurm should then connect you to the remote cluster to query its status

This workflow should work while maintaining the compatibility with the workflow consisting in connecting with tramp, then M-x slurm.

This PR closes #8.

[aancel]

Hello, Coming back to this MR, did you get some time to test it ? (Or will you have some in the coming weeks ?)

Thanks a lot !