Pyenv-virtualenv: Add a --skip-existing option when creating a virtualenv

[myers]

I would like pyenv virtualenv --skip-existing 3.4.3 photos to skip making the photos virutalenv if it already exists, much like pyenv install --skip-existing 3.4.3 skips installing 3.4.3 if it's installed.

[yyuu]

Use [ -d "$(pyenv root)/versions/3.4.3" ] instead.

[rmorshea]

This solution seems to have gotten a lot of downvotes. Perhaps it's worth reconsidering.