Remove unused create_image of Nova v2 API

There are two create_image methods for Nova v2 API, but the one of
images_client.py only is used in most cases.
This patch removes the unused create_image of servers_client.py.

Change-Id: Icd457b6693c076c5c8b9d48bb88da162161c9a1a
Merge "Remove unused create_image of Nova v2 API"