Adds instance evacuation api documentation.

The documentation contains details about required parameters of
evacuate api

blueprint rebuild-for-ha

Change-Id: Ie50b70004ce20b397f9a22165d1c6a313f0d4be9
Adding os-ext-img-size extension to compute extensions

bug: #1128543

Change-Id: I40ee96dfa9b18b50cfa318e9992ca30e04b19d01
author: Diane Fleming
Merge "Adds instance evacuation api documentation."
Updated code samples for os-services extension

bug: #1104264

Change-Id: I8c2dde7a912c6833683c0824de041104e0a8b7ca
author: Diane Fleming