devmapper: udev sync in `docker info`

now:

```
[...]
Storage Driver: devicemapper
 Pool Name: docker-253:2-5767172-pool
 [...]
 Udev Sync Supported: true
[...]
```

Signed-off-by: Vincent Batts <vbatts@redhat.com>

daemon/graphdriver/devmapper/deviceset.go

@@ -105,14 +105,15 @@ type DiskUsage struct {
 }
 
 type Status struct {
-	PoolName         string
-	DataFile         string // actual block device for data
-	DataLoopback     string // loopback file, if used
-	MetadataFile     string // actual block device for metadata
-	MetadataLoopback string // loopback file, if used
-	Data             DiskUsage
-	Metadata         DiskUsage
-	SectorSize       uint64
+	PoolName          string
+	DataFile          string // actual block device for data
+	DataLoopback      string // loopback file, if used
+	MetadataFile      string // actual block device for metadata
+	MetadataLoopback  string // loopback file, if used
+	Data              DiskUsage
+	Metadata          DiskUsage
+	SectorSize        uint64
+	UdevSyncSupported bool
 }
 
 type DevStatus struct {
@@ -1578,6 +1579,7 @@ func (devices *DeviceSet) Status() *Status {
 	status.DataLoopback = devices.dataLoopFile
 	status.MetadataFile = devices.MetadataDevicePath()
 	status.MetadataLoopback = devices.metadataLoopFile
+	status.UdevSyncSupported = devicemapper.UdevSyncSupported()
 
 	totalSizeInSectors, _, dataUsed, dataTotal, metadataUsed, metadataTotal, err := devices.poolStatus()
 	if err == nil {

daemon/graphdriver/devmapper/driver.go

@@ -74,6 +74,7 @@ func (d *Driver) Status() [][2]string {
 		{"Data Space Total", fmt.Sprintf("%s", units.HumanSize(float64(s.Data.Total)))},
 		{"Metadata Space Used", fmt.Sprintf("%s", units.HumanSize(float64(s.Metadata.Used)))},
 		{"Metadata Space Total", fmt.Sprintf("%s", units.HumanSize(float64(s.Metadata.Total)))},
+		{"Udev Sync Supported", fmt.Sprintf("%v", s.UdevSyncSupported)},
 	}
 	if len(s.DataLoopback) > 0 {
 		status = append(status, [2]string{"Data loop file", s.DataLoopback})