[all] Change warranty date format (YYYY-MM-DD)

data/grid5000/sites/grenoble/servers/alpes.json

data/grid5000/sites/grenoble/servers/dighyp1.json

data/grid5000/sites/grenoble/servers/dighyp2.json

data/grid5000/sites/grenoble/servers/digmgt.json

data/grid5000/sites/grenoble/servers/dignfs.json

data/grid5000/sites/grenoble/servers/digsed.json

...grid5000/sites/lille/network_equipments/sw-chiclet-1.json

...grid5000/sites/lille/network_equipments/sw-chiclet-2.json

...grid5000/sites/lille/network_equipments/sw-chiclet-3.json

data/grid5000/sites/lille/servers/carbonade.json

data/grid5000/sites/lille/servers/caulier.json

data/grid5000/sites/lille/servers/chimint-srv2.json

data/grid5000/sites/lille/servers/chiterne.json

data/grid5000/sites/lille/servers/fives.json

data/grid5000/sites/lille/servers/flandres.json

data/grid5000/sites/lille/servers/srv-data.json

data/grid5000/sites/lille/servers/welsh.json

...00/sites/luxembourg/network_equipments/gw-luxembourg.json

data/grid5000/sites/luxembourg/servers/cronos.json

data/grid5000/sites/luxembourg/servers/hera.json