- TS_low_dummy was introcuced in PR69 but we already had a mechanism for
it (using the `runOnce` flag.
- The check of the output of turbsim was there before and was removed on
  PR69, only checking the presence and non-zero-bytes value of the
  output files. Now we put the check back. PR69 handles the errors in a
  different way and thus wouldn't need this check, but when using SLURM
  scripts it is still needed

the skipcheck flag allows us to test all the way to FF_setup, as opposed
to stopping at the low-res generation

Removed in PR69, now added back in a more robust way. Just checking the
existence of the file is not enough.