Collectors in parallel (#74)

* Provide info to CollectorManager whether the collector can be executed in parallel with others

* Split serial and parallel collectors. Read in parallel first

collectors/diskstatMetric.go

@@ -29,6 +29,7 @@ type DiskstatCollector struct {
 
 func (m *DiskstatCollector) Init(config json.RawMessage) error {
 	m.name = "DiskstatCollector"
+	m.parallel = true
 	m.meta = map[string]string{"source": m.name, "group": "Disk"}
 	m.setup()
 	if len(config) > 0 {
@@ -77,7 +78,11 @@ func (m *DiskstatCollector) Read(interval time.Duration, output chan lp.CCMetric
 			continue
 		}
 		path := strings.Replace(linefields[1], `\040`, " ", -1)
-		stat := syscall.Statfs_t{}
+		stat := syscall.Statfs_t{
+			Blocks: 0,
+			Bsize:  0,
+			Bfree:  0,
+		}
 		err := syscall.Statfs(path, &stat)
 		if err != nil {
 			continue
@@ -98,9 +103,11 @@ func (m *DiskstatCollector) Read(interval time.Duration, output chan lp.CCMetric
 			y.AddMeta("unit", "GBytes")
 			output <- y
 		}
-		perc := (100 * (total - free)) / total
-		if perc > part_max_used {
-			part_max_used = perc
+		if total > 0 {
+			perc := (100 * (total - free)) / total
+			if perc > part_max_used {
+				part_max_used = perc
+			}
 		}
 	}
 	y, err := lp.New("part_max_used", map[string]string{"type": "node"}, m.meta, map[string]interface{}{"value": int(part_max_used)}, time.Now())