Use LongName for FP collection descriptions in pyrob

[mathomp4]

Per a request of @rlucches, for Forward Processing (-F) runs, pyrob now derives the collection description from the LongName global attribute of the netCDF file, stripping any leading 'GEOS FP ' prefix and title-casing the result.

A new --no-longname flag restores the legacy Title-based behavior for older FP (and GEOS-IT) files that predate the LongName attribute.

I tested this on a couple files:

Old behavior (--no-longname):

pyrob -F -v -H HISTORY.rc -f stdout --no-longname GEOS.fp.*.nc4
1) Collection inst1_2d_lfo_Nx (DFPI1NXLFO): Land Surface Forcings
2) Collection inst3_2d_asm_Nx (DFPI3NXASM): Single-Level Diagnostics

New default behavior (from LongName global attribute):

pyrob -F -v -H HISTORY.rc -f stdout GEOS.fp.*.nc4
1) Collection inst1_2d_lfo_Nx (DFPI1NXLFO): 2D Time-Averaged Land Surface Forcing
2) Collection inst3_2d_asm_Nx (DFPI3NXASM): 2D Assimilated State