GitLab

* Added some exception handling when a site is down.
* Ask before making reservation on the whole platform when the script is used without any argument
* With -n, only attempt a reservation if the node belong to the site
* Manage both -n node.site.grid5000.fr and -n node format
* Removed an unneeded duplicated call to the API

fixed according to the DCHP entries

* this option still checks if the node is busy
* I also improved ssh error handling
* I also added -s, -c, -n, -q, --ssh-keys, -h options