Make copy_to_volume a bit more useful.

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