Unable to perform queries through mongos
Well, finally I've solved the problem. It was my fault when configuring everything to give the same name data to the replicas of the config server and the sharded server.

I replaced data by rs0 when launching the config servers:

mongod --configsvr --replSet rs0 --bind_ip localhost,${HOSTNAME}\
    --port 25000 --logpath /var/lib/mongodb/shardedcluster/log.cfg\
    --logappend --dbpath /var/lib/mongodb/shardedcluster/cfg --fork


Of course in the first rs.initiate changed _id to rs0 and finally when launching the mongos replaced data with rs0:

mongos --configdb data/mongoserver1:25000,mongoserver2:25000,mongoserver3:25000 \
    --bind_ip localhost,${HOSTNAME} \
    --logpath /var/lib/mongodb/shardedcluster/mongos.log --fork


Now it works like charm :)