image(s) schema image metadata API test

This patch is added to test get_images_schema and get_image_schema
image metadata APIs.
In addition to this, it changes the client function written for
these APIs.
A single method is written to merge all the schema client methods,
thus giving better way to code utilization.

Change-Id: I0fbd557e7abb7227b94488b270760858e0f32ca4
Merge "image(s) schema image metadata API test"