Use the device name as the GRES type instead of the brand name

Base GRES type off of device name instead of brand name.
Make the device name lower case and replace spaces with underscores.
Truncate system-detected device names so they match GRES types in
slurm.conf (important for FastSchedule 0 and 1).

Bug 7345

Co-authored-by: Michael Hinton <hinton@schedmd.com>