Add API sample files of "unshelve a server" API

Now there are not API sample files of "unshelve a server" and
"shelve-offload" APIs, and OpenStack API documentation also
does not show these APIs.
This patch adds these API sample files.

DocImpact
Closes-Bug: #1285482

Change-Id: Idf797eb6723b94abae71a77c12bc2bb9b330fa28
Merge "Add API sample files of "unshelve a server" API"