CSET conda environment could be wiped on $SCRATCH without checks

[jwarner8]

Something else

A potential issue is if scratch is chosen to build the conda env, as the 30 day housekeeping comes round various libraries will be deleted leading to weird error messages. CSET sees the directory exists and performs no checks "Conda environment already exist, no build required" and assumes OK. Could add some checksum to make sure all files exist, but this could be quite slow. Note this is an issue that affects Met Office systems only (although partners may have similar policies for data directories).