Check that current directory isn't getting removed in calls to shtutils.rmtree...

[ekluzek]

With run_neon there is a directory tree removal that should add some error checking to it. It should make sure the directory being used isn't the current one.

ctsm/site_and_regional/neon_site.py:            shutil.rmtree(case_path)
ctsm/site_and_regional/neon_site.py:                shutil.rmtree(case_root)

#2363 has this as well, but the code was just moved to a new location, so doesn't introduce it.

[ekluzek]

This also relates to #2405. There is a proposal there to add a small utility for this, that would be a good way to handle this.

But, I think we should get a check in place right away and refactor when the utility is added at a later date.