Check if dir exist before creating a dir in biconda-recipes

[Hogfeldt]

If a directory already exists in bioconda-recipes/recipes whit the name of that package which we trying to build, the sanity check crashes the program.

[Hogfeldt]

It seems like we are cleaning up the directory in a proper way. But it seems like there is some cases where it goes wrong.

[JesperBrink]

Seems that the times the program crashes is because we manually creates a folder with that name for testing purpose, and just forgot to delete it.
Keeping the issue open for now, in case we find another reason.