Nova compute raises AttributeError on creating a new instance with raw
image format leading instance to go in to error state. This bug is
introduced by commit I34e2f29e1f068636036226a7745d88640f724d93 which
added image.file in disk api instead of image.path.
Changed image.file to image.path to fix this issue.
Closes-Bug: 1470356
Change-Id: I4a12263a992eaf8abf2e90089591051d5aa57585
3f6df2d7c1