Make copy_to_volume a bit more useful.

The current implementation of cinder.driver.copy_to_volume
does not take in to account image type and is only valid
for raw images.  This doesn't do much good for the majority
of cases, and rather than require folks to have a raw version
uploaded to Glance, let's just do a convert if needed on the fly.

This simply creates a temp file, does the conversion and then
writes the temp file directly to the volume.

Change-Id: I849b04b8aae76da068abcd2a20c1fcecca8a5caa

cinder/volume/driver.py

@@ -26,6 +26,7 @@ import time
 
 from cinder import exception
 from cinder import flags
+from cinder.image import image_utils
 from cinder.openstack.common import cfg
 from cinder.openstack.common import log as logging
 from cinder import utils
@@ -586,10 +587,10 @@ class ISCSIDriver(VolumeDriver):
 
     def copy_image_to_volume(self, context, volume, image_service, image_id):
         """Fetch the image from image_service and write it to the volume."""
-        volume_path = self.local_path(volume)
-        with utils.temporary_chown(volume_path):
-            with utils.file_open(volume_path, "wb") as image_file:
-                image_service.download(context, image_id, image_file)
+        image_utils.fetch_to_raw(context,
+                                 image_service,
+                                 image_id,
+                                 self.local_path(volume))
 
     def copy_volume_to_image(self, context, volume, image_service, image_id):
         """Copy the volume to the specified image."""