Hang at exit if an invalid scheduler_headnode value is provided to slurm launcher

[mkundu1]

>>> import ansys.fluent.core as pyfluent
>>> slurm = pyfluent.launch_fluent(scheduler_options={"scheduler": "slurm", "scheduler_headnode": "nonsense"}, ui_mode="no_gui_or_graphics")
ssh: Could not resolve hostname nonsense: Name or service not known
>>> exit()  # hangs

This issue was originally reported in PyConsole (Fluent bug 1115063).