Use relative paths for NEON datasets to make them more readable

[ekluzek]

Filenames for the NEON datasets are especially long for tests since it uses an absolute path for $RUNDIR and then includes deep subdirectories beneath that.

See this discussion here...

ESCOMP/CTSM#2310 (comment)

This is related to #263. As above this changes the path from:

/derecho/scratch/erik/tests_alpha-ctsm52mksrf25_ctsm51d174acl/SMS_Ld10_D_Mmpi-serial.CLM_USRDAT.I1PtClm51Fates.derecho_intel.clm-FatesFireLightningPopDens--clm-NEON-FATES-NIWO.GC.alpha-ctsm52mksrf25_ctsm51d174acl_int/run/inputdata/atm/cdeps/v2/NIWO/NIWO_atm_2018-01.nc

to:

inputdata/atm/cdeps/v2/NIWO/NIWO_atm_2018-01.nc

which is just so much easier to read.

[ekluzek]

This might be something for @TeaganKing to take on along with other parts of her NEON work. We'll decide later...