Convert CamelCase attribute naming to camel_case for servers V3 API

Convert cases of CamelCase attribute naming to camel_case in the
servers V3 API to make the v3 API as whole consistent in the naming
of attributes

Partially implements blueprint nova-v3-api

Change-Id: Ie2c790ae8eb01f02d754911b0a10c4061d0b4a92
Merge "Convert CamelCase attribute naming to camel_case for servers V3 API"