pyenv virtualenv-reset - Reset a virtual environment to an initial state

[erezh16]

This is an enhancement proposal that I would find quite useful.

I use pyenv with virtual envs all the time. Quite convenient to set both the Python version, tooling and packages in one place.
One common issue I have it that I would like to use the same virtual env several times, starting from scratch, e.g., when testing installation configurations.

I propose to add a new command, pyenv virtualenv-reset [<venv>] that would do the following:

1. Delete the venv (deactivate it first if active)
2. Re-create the venv with the same Python version that it had before
3. If venv was initially active, activate it again automatically

If venv is not provided, the currently-active venv is selected for reset