Fix sheepdog copy_image_to_volume method

The sheepdog driver fails when trying to
create volume from image due to a bug in
SheepdogDriver.copy_image_to_volume.

The utils.convert method is being passed the
tempfile object, but should only be passed
the name of the tempfile.

Change-Id: I6b261d29895bf9c2c30b2d95d74e5be58b8e9b10
Closes-Bug: 1261941
Merge "Fix sheepdog copy_image_to_volume method"