Do not support 2 jails with same name, only keep the first seen

cmd/list.go

@@ -220,6 +220,15 @@ func listJailsFromDirectory(dir string) []Jail {
 				j.Zpool = strings.Split(strings.TrimSuffix(out, "\n"), "/")[0]
 			}
 
+			// Check if jail with the same name already exist on another DS
+			for _, jj := range gJails {
+				if strings.EqualFold(jj.Name, j.Name) {
+					fmt.Printf("ERROR: A jail with name %s already exist on datastore %s!\n", j.Name, jj.Zpool)
+					fmt.Printf("Jail %s on datastore %s wont be handled\n", j.Name, j.Zpool)
+					return gJails
+				}
+			}
+
 			gJails = append(gJails, j)
 		}
 	}