Add HostID to the Host InfoStat struct returned from host.Info().

On supported hosts the value returned is a UUID (case preserving
from the value of the underlying OS).

For Linux this is generated once, randomly per boot.  For FreeBSD and
Darwin this is a more durable value that should persist across reboots.

host/host.go

@@ -25,7 +25,7 @@ type InfoStat struct {
 	PlatformVersion      string `json:"platformVersion"`
 	VirtualizationSystem string `json:"virtualizationSystem"`
 	VirtualizationRole   string `json:"virtualizationRole"` // guest or host
-
+	HostID               string `json:"hostid"`             // ex: uuid
 }
 
 type UserStat struct {

host/host_darwin.go

@@ -56,6 +56,11 @@ func Info() (*InfoStat, error) {
 		ret.Procs = uint64(len(procs))
 	}
 
+	values, err := common.DoSysctrl("kern.uuid")
+	if err == nil && len(values) == 1 && values[0] != "" {
+		ret.HostID = values[0]
+	}
+
 	return ret, nil
 }
 

host/host_freebsd.go

@@ -59,6 +59,11 @@ func Info() (*InfoStat, error) {
 		ret.Procs = uint64(len(procs))
 	}
 
+	values, err := common.DoSysctrl("kern.hostuuid")
+	if err == nil && len(values) == 1 && values[0] != "" {
+		ret.HostID = values[0]
+	}
+
 	return ret, nil
 }
 

host/host_linux.go

@@ -61,6 +61,11 @@ func Info() (*InfoStat, error) {
 		ret.Procs = numProcs
 	}
 
+	values, err := common.DoSysctrl("kernel.random.boot_id")
+	if err == nil && len(values) == 1 && values[0] != "" {
+		ret.HostID = values[0]
+	}
+
 	return ret, nil
 }
 

host/host_test.go

@@ -66,8 +66,9 @@ func TestHostInfoStat_String(t *testing.T) {
 		OS:       "linux",
 		Platform: "ubuntu",
 		BootTime: 1447040000,
+		HostID:   "edfd25ff-3c9c-b1a4-e660-bd826495ad35",
 	}
-	e := `{"hostname":"test","uptime":3000,"bootTime":1447040000,"procs":100,"os":"linux","platform":"ubuntu","platformFamily":"","platformVersion":"","virtualizationSystem":"","virtualizationRole":""}`
+	e := `{"hostname":"test","uptime":3000,"bootTime":1447040000,"procs":100,"os":"linux","platform":"ubuntu","platformFamily":"","platformVersion":"","virtualizationSystem":"","virtualizationRole":"","hostid":"edfd25ff-3c9c-b1a4-e660-bd826495ad35"}`
 	if e != fmt.Sprintf("%v", v) {
 		t.Errorf("HostInfoStat string is invalid: %v", v)
 	}