Problems with LS2 files: needs check across all files

[agstephens]

Two issues identified with the file sandpit/example_data/ukcp18/data/land-gcm/uk/60km/rcp85/22/huss/mon/latest/huss_rcp85_land-gcm_uk_60km_22_mon_189912-209911.nc:

1. “latitude” and “longitude” are missing as coordinate variables
2. The “ensemble_member” value is 21 in the file but is 22 in the file name.
3. The “ensemble_member_id” string does not match any found in the vocabs: https://github.com/ukcp-data/UKCP18_CVs/blob/master/UKCP18_CVs/UKCP18_ensemble_member.json