Comment 9 for bug 1350766

The patch was proposed in the very beginning, see https://bugs.launchpad.net/nova/+bug/1350766/+attachment/4166489/+files/nova-glance.patch

It's copies a snipplet of utils code from swift, in order not to introduce a cross service dependency. The actual fix is then a one-liner: fsync the image before returning from download.

The modification itself is quite self contained. Whether the style is acceptable needs review. But should be low hanging fruit.