Refactor stats and add them to all subsystems

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

cgroups/fs/memory.go

@@ -2,7 +2,6 @@ package fs
 
 import (
 	"bufio"
-	"fmt"
 	"os"
 	"path/filepath"
 	"strconv"
@@ -51,19 +50,20 @@ func (s *memoryGroup) Stats(d *data) (map[string]float64, error) {
 	paramData := make(map[string]float64)
 	path, err := d.path("memory")
 	if err != nil {
-		fmt.Errorf("Unable to read %s cgroup param: %s", path, err)
-		return paramData, err
+		return nil, err
 	}
+
 	f, err := os.Open(filepath.Join(path, "memory.stat"))
 	if err != nil {
-		return paramData, err
+		return nil, err
 	}
 	defer f.Close()
+
 	sc := bufio.NewScanner(f)
 	for sc.Scan() {
 		t, v, err := getCgroupParamKeyValue(sc.Text())
 		if err != nil {
-			return paramData, fmt.Errorf("Error parsing param data: %s", err)
+			return nil, err
 		}
 		paramData[t] = v
 	}