Allow ramdisk_id, kernel_id to be null on schema
Allow ramdisk_id, kernel_id to be null on schema

Since is possible to create images with no
ramdisk_id, kernel_id parameters on glance v1,
then the schema-image.json needs to be modified to
allow null, string values for both attributes
and prevent LP #1447193 to happen with a glance v2
client.

APIImpact

Closes-Bug: #1447215
Related-Bug: #1447193

Change-Id: I645c797553ccaa84062f9ad28f2349ae738a0c96
Signed-off-by: Jorge Niedbalski <c306b413ed4d10f0564ceec57804dfc191869a8a@canonical.com>
(cherry picked from commit 82c63b1df4399db22dfd71e3326a6bfc1b372a9c)

darren-wang/gl,darren-wang/gl