Fix for reading the xenapi_device_id from image metadata

The xenapi_device_id is set on the image metadata.
This is used to set the device_id on the vm record
before the vm is created. Currently, when we read
the device id from the metadata we are looking at
the key image_meta["xenapi_device_id"].
But the device id is set as
image_meta["properties"]["xenapi_device_id"].

Fixes bug 1253564

Change-Id: Ide174b50db4e440401b5e6389844e7dcfc8a1c76
Merge "Fix for reading the xenapi_device_id from image metadata"