[nantes] add flops values for ecotype

input/grid5000/sites/nantes/clusters/ecotype/ecotype.yaml

@@ -11,6 +11,9 @@ nodes:
   ecotype-[1-48]:
     processor:
       microarchitecture: Broadwell
+    performance:
+      core_flops:  13180000000
+      node_flops: 275300000000
     supported_job_types:
       deploy: true
       besteffort: false