Add system uptime metric, string formatted AND in float64

closes #150

CHANGELOG.md

@@ -2,7 +2,8 @@
 
 ### Features
 
-[#158](https://github.com/influxdb/telegraf/pull/158): Apache Plugin
+[#155](https://github.com/influxdb/telegraf/pull/155): Add Host Uptime metric to system plugin
+[#158](https://github.com/influxdb/telegraf/pull/158): Apache Plugin. Thanks @KPACHbIuLLIAnO4
 
 ### Bugfixes
 

plugins/system/system.go

@@ -1,13 +1,17 @@
 package system
 
-import "github.com/influxdb/telegraf/plugins"
+import (
+	"github.com/cloudfoundry/gosigar"
+
+	"github.com/influxdb/telegraf/plugins"
+)
 
 type SystemStats struct {
 	ps PS
 }
 
 func (_ *SystemStats) Description() string {
-	return "Read metrics about system load"
+	return "Read metrics about system load & uptime"
 }
 
 func (_ *SystemStats) SampleConfig() string { return "" }
@@ -21,13 +25,19 @@ func (s *SystemStats) add(acc plugins.Accumulator,
 
 func (s *SystemStats) Gather(acc plugins.Accumulator) error {
 	lv, err := s.ps.LoadAvg()
+	uptime := sigar.Uptime{}
 	if err != nil {
 		return err
 	}
+	if err := uptime.Get(); err != nil {
+		return err
+	}
 
 	acc.Add("load1", lv.Load1, nil)
 	acc.Add("load5", lv.Load5, nil)
 	acc.Add("load15", lv.Load15, nil)
+	acc.Add("uptime", uptime.Length, nil)
+	acc.Add("uptime_format", uptime.Format(), nil)
 
 	return nil
 }