Refactor stats and add them to all subsystems

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

cgroups/fs/utils.go

@@ -1,23 +1,25 @@
 package fs
 
 import (
+	"errors"
 	"fmt"
 	"strconv"
 	"strings"
 )
 
+var ErrNotSupportStat = errors.New("stats are not supported for subsystem")
+
 // Parses a cgroup param and returns as name, value
 //  i.e. "io_service_bytes 1234" will return as io_service_bytes, 1234
 func getCgroupParamKeyValue(t string) (string, float64, error) {
 	parts := strings.Fields(t)
 	switch len(parts) {
 	case 2:
-		name := parts[0]
 		value, err := strconv.ParseFloat(parts[1], 64)
 		if err != nil {
 			return "", 0.0, fmt.Errorf("Unable to convert param value to float: %s", err)
 		}
-		return name, value, nil
+		return parts[0], value, nil
 	default:
 		return "", 0.0, fmt.Errorf("Unable to parse cgroup param: not enough parts; expected 2")
 	}