Create image api does not show all required or optional attributes.

"name" and "metadata" only occurs in the example,
but they are not specified in the "Request parameters" section.
there is no doc to indicate that if them are required or optional.

Fix bug 1158134

Change-Id: Iacf6df91e4633a32a2c6b31b9d3d660299ad800a
Merge "Create image api does not show all required or optional attributes."