Update the repository deletion and disable false warnings

[JeremyLr]

1. Add of a non-digit check for the key in v2/repositories.py
2. Update of the do_repository_delete in the v2/shell.py because the previous function did not work. Note : the do_tags_delete does not work too (the deletion of one tag, delete all the tags) because of an issue with the listing functions I think, but for the moment I could not investigate more to fix it...
3. Workaround : add an import library to disable the list of false SSL certificate warnings using Python 2.7