[environments] Used available_on method to update environments present on sites.

...grid5000/sites/orsay/environments/lenny-x64-base-2.1.json

...grid5000/sites/orsay/environments/lenny-x64-base-2.2.json

.../grid5000/sites/orsay/environments/lenny-x64-big-2.1.json

.../grid5000/sites/orsay/environments/lenny-x64-big-2.2.json

.../grid5000/sites/orsay/environments/lenny-x64-nfs-2.1.json

.../grid5000/sites/orsay/environments/lenny-x64-nfs-2.2.json

data/grid5000/sites/orsay/orsay.json

...rid5000/sites/rennes/environments/lenny-x64-base-2.1.json

...rid5000/sites/rennes/environments/lenny-x64-base-2.2.json

...grid5000/sites/rennes/environments/lenny-x64-big-2.1.json

...grid5000/sites/rennes/environments/lenny-x64-big-2.2.json

...grid5000/sites/rennes/environments/lenny-x64-nfs-2.1.json

...grid5000/sites/rennes/environments/lenny-x64-nfs-2.2.json

...rid5000/sites/sophia/environments/lenny-x64-base-2.1.json

...rid5000/sites/sophia/environments/lenny-x64-base-2.2.json

...grid5000/sites/sophia/environments/lenny-x64-big-2.1.json

...grid5000/sites/sophia/environments/lenny-x64-big-2.2.json

...grid5000/sites/sophia/environments/lenny-x64-nfs-2.1.json

...grid5000/sites/sophia/environments/lenny-x64-nfs-2.2.json

...id5000/sites/toulouse/environments/etch-x64-base-2.0.json