[grenoble/servan] Add initial configuration for servan

...id5000/sites/grenoble/clusters/servan/nodes/servan-1.json

...id5000/sites/grenoble/clusters/servan/nodes/servan-2.json

data/grid5000/sites/grenoble/clusters/servan/servan.json

data/grid5000/sites/grenoble/network_equipments/gw.json

input/grid5000/disks.yaml

input/grid5000/ipv4.yaml

...id5000/sites/grenoble/clusters/servan/nodes/servan-1.yaml

...id5000/sites/grenoble/clusters/servan/nodes/servan-2.yaml

input/grid5000/sites/grenoble/clusters/servan/servan.yaml

input/grid5000/sites/grenoble/networks/gw-grenoble.yaml

lib/refrepo/net_names_mapping.yaml