Absolute path for variant_dir

[bthe]

When defining a model variant for projections I would like to store the interim results in a temporary via tempdir(). Since gadget.variant.dir assumes the variant_dir is specified relative to the model directory the definition of the tempdir() as the variant_dir becomes fairly clumsy. Assuming no knowledge of the current working directory this can be hacked with:

getwd() %>% 
      stringr::str_count('/') %>% 
      rep('../',.) %>% 
      paste(collapse = '') %>% 
      paste(tempdir(),sep='')

But I assume it would be simpler to change gadget.variant.dir such that absolute positioning of the variant directory can be allowed.