Backport ResumeDevice() from master

Kazuyoshi Kato · Kazuyoshi Kato · commit c2cf0570096e · 2020-07-09T13:26:32.000-07:00
The previous cherry-picked change (81acbcf) doesn't work without this function.
diff --git a/snapshots/devmapper/pool_device.go b/snapshots/devmapper/pool_device.go
@@ -359,6 +359,16 @@ func (p *PoolDevice) SuspendDevice(ctx context.Context, deviceName string) error
 	return nil
 }
 
+func (p *PoolDevice) ResumeDevice(ctx context.Context, deviceName string) error {
+	if err := p.transition(ctx, deviceName, Resuming, Resumed, func() error {
+		return dmsetup.ResumeDevice(deviceName)
+	}); err != nil {
+		return errors.Wrapf(err, "failed to resume device %q", deviceName)
+	}
+
+	return nil
+}
+
 // DeactivateDevice deactivates thin device
 func (p *PoolDevice) DeactivateDevice(ctx context.Context, deviceName string, deferred, withForce bool) error {
 	if !p.IsLoaded(deviceName) {
