Handle system UUID retrieval for Power(ppc64) Systems

This patch adds requisite support to retrieve system uuid details for Power
systems. Power systems do not have DMI data. However most of the relevant details
are either in /proc or /sys. For baremetal servers, the UID is available in
/proc/device-tree/system-id. For guests the UUID is available in
/proc/device-tree/vm,uuid inside the guest. Guest's /proc filesystem do not have
/proc/device-tree/system-id

Example
On baremetal system
$cat /proc/device-tree/system-id
2122AAA

On a guest VM
$cat /proc/device-tree/vm,uuid
4b1a1a7e-079e-479c-8072-d8108f31050c

Signed-off-by: Pradipta Kr. Banerjee <bpradip@in.ibm.com>

utils/sysfs/sysfs.go

@@ -24,10 +24,11 @@ import (
 )
 
 const (
-	blockDir = "/sys/block"
-	cacheDir = "/sys/devices/system/cpu/cpu"
-	netDir   = "/sys/class/net"
-	dmiDir   = "/sys/class/dmi"
+	blockDir   = "/sys/block"
+	cacheDir   = "/sys/devices/system/cpu/cpu"
+	netDir     = "/sys/class/net"
+	dmiDir     = "/sys/class/dmi"
+	ppcDevTree = "/proc/device-tree"
 )
 
 type CacheInfo struct {
@@ -235,7 +236,15 @@ func (self *realSysFs) GetCacheInfo(id int, name string) (CacheInfo, error) {
 func (self *realSysFs) GetSystemUUID() (string, error) {
 	id, err := ioutil.ReadFile(path.Join(dmiDir, "id", "product_uuid"))
 	if err != nil {
-		return "", err
+		//If running on baremetal Power then UID is /proc/device-tree/system-id
+		id, err = ioutil.ReadFile(path.Join(ppcDevTree, "system-id"))
+		if err != nil {
+			//If running on a KVM guest on Power then UUID is /proc/device-tree/vm,uuid
+			id, err = ioutil.ReadFile(path.Join(ppcDevTree, "vm,uuid"))
+			if err != nil {
+				return "", err
+			}
+		}
 	}
 	return strings.TrimSpace(string(id)), nil
 }