robustify conda checks in configure_conda script
- 'which conda' result does not seems enough to check that conda is correctly installed since 'activate conda' may not work if the shell configuration file (.bashrc, ..) is not properly configured
[A venir] Mise en place de quotas sur nos instances GitLab. Plus d'information sur : https://doc-si.inria.fr/pages/viewpage.action?pageId=129728565
[Coming soon] Quotas installation on our GitLab instances. More information: https://doc-si.inria.fr/pages/viewpage.action?pageId=129728565