detect & create conda environments

[lmmarsano]

pyenv virtualenv fails to create conda environments from conda environments.

$ pyenv virtualenv lsp test
Looking in links: /tmp/tmp0ao0gi5w
Requirement already satisfied: setuptools in /home/LOM0227/.pyenv/versions/miniconda3-latest/envs/test/lib/python3.7/site-packages (40.8.0)
Requirement already satisfied: pip in /home/LOM0227/.pyenv/versions/miniconda3-latest/envs/test/lib/python3.7/site-packages (19.0.3)
$ pyenv versions
* system (set by /home/LOM0227/.pyenv/version)
  lsp
  miniconda3-latest
  miniconda3-latest/envs/lsp
  miniconda3-latest/envs/test
  test
$ conda info -e
# conda environments:
#
base                  *  /home/LOM0227/.pyenv/versions/miniconda3-latest
lsp                      /home/LOM0227/.pyenv/versions/miniconda3-latest/envs/lsp

Instead, it attempts to make python venv environments. These updates reuse logic from #290 to detect conda environments, detect conda base environments, and clone non-base environments supplied as version to pyenv virtualenv.